Battery cell, battery device, and electric device

Abstract

The invention provides a battery monomer, a battery device and a power utilization device.The battery monomer comprises an electrode assembly, and the electrode assembly comprises a negative pole piece; the negative electrode plate comprises a negative electrode current collector, and the negative electrode current collector comprises a negative electrode current collecting part and a negative electrode lug extending out of the negative electrode current collecting part in the first direction; the negative electrode film layer is positioned on at least one side of the negative electrode current collecting part; the size w1 of the negative electrode tab in the second direction and the size w2 of the electrode assembly in the second direction meet the condition that w1 / w2 is greater than or equal to 15% and less than or equal to 30%; the first direction is the width direction of the negative pole piece, and the second direction is the length direction of the negative pole piece. The battery monomer provided by the invention has excellent quick charge performance and cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery monomer, a battery device and a power utilization device. BACKGROUND

[0002] In recent years, with the application range of secondary batteries becoming more and more extensive, secondary batteries are widely used in energy storage power supply systems such as water, fire, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. With the rapid development of secondary batteries, people have higher requirements for the fast charging performance and cycle performance of secondary batteries.

[0003] Therefore, how to make the secondary battery have excellent fast charging performance and cycle performance has become a technical problem to be solved. SUMMARY

[0004] The present application is carried out in view of the above-mentioned problems, and aims to provide a battery monomer, a battery device and a power utilization device, the battery monomer of the present application has excellent fast charging performance and cycle performance.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a battery monomer, comprising an electrode assembly, the electrode assembly comprising a negative electrode sheet; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer, the negative electrode current collector comprises a negative electrode current collecting part and a negative electrode tab extending from the negative electrode current collecting part along a first direction; the negative electrode film layer is located on at least one side of the negative electrode current collecting part; the size w1 of the negative electrode tab in the second direction and the size w2 of the electrode assembly in the second direction satisfy: 15%≤w1 / w2≤30%; the first direction is the width direction of the negative electrode sheet, and the second direction is the length direction of the negative electrode sheet.

[0006] This application satisfies the aforementioned conditions by limiting the dimensions w1 of the negative electrode tab in the second direction and w2 of the electrode assembly in the second direction. This results in a wider negative electrode tab within a suitable range, optimizing the current distribution density on the negative electrode tab while meeting processing requirements and safety performance, thereby reducing the current density on the negative electrode tab. Specifically, current density = current / conductive area. For the same current, a wider negative electrode tab results in a larger negative electrode tab area, thus reducing the current density per unit area of ​​the negative electrode tab. This reduced current density on the negative electrode tab leads to a corresponding decrease in the current density flowing into the negative electrode current collector, and consequently, a decrease in the current density transferred to the negative electrode film. Therefore, the current per unit area of ​​the negative electrode film is smaller, which helps to reduce the lithium intercalation reaction rate per unit negative electrode film. The reduced lithium intercalation reaction rate, on the one hand, lowers the activation energy barrier required for charge transfer of lithium ions through the electrode or electrolyte interface, reducing the activation overpotential; on the other hand, it ensures that the lithium ion diffusion rate meets the reaction requirements, reducing the concentration overpotential. Therefore, reducing the current density per unit area of ​​the negative electrode film can decrease the overpotential for lithium intercalation at the tab side, thereby improving lithium plating. Improved lithium plating benefits both by enhancing lithium intercalation kinetics, thus improving the fast-charging performance of the battery cell, and by reducing the probability of side reactions with the electrolyte, thereby reducing heat generation and improving the cycle life of the battery cell. Furthermore, the reduced current density at the tab can also reduce heat generation at the tab, further decreasing the probability of side reactions at the tab and further improving the cycle performance of the battery cell.

[0007] In some embodiments, the dimension w1 of the negative electrode tab in the second direction and the dimension w2 of the electrode assembly in the second direction satisfy: 17% ≤ w1 / w2 ≤ 28%. This is more conducive to optimizing the current distribution density on the negative electrode tab while meeting processing requirements and safety performance, thereby further improving lithium plating and further benefiting the fast-charging performance and cycle performance of the battery cell.

[0008] In some embodiments, the dimension w1 of the negative electrode tab in the second direction is 30 mm to 60 mm. In some embodiments, the dimension w1 of the negative electrode tab in the second direction is 35 mm to 55 mm. This reduces the current density per unit area of ​​the tab, thereby lowering the lithium insertion reaction rate in the negative electrode film per unit area, improving lithium plating, and further enhancing the fast-charging and cycle performance of the battery cell. Furthermore, it does not affect the subsequent welding process and does not overlap with the positive electrode tab, further improving the processing performance and safety performance of the battery cell.

[0009] In some embodiments, the size L1 of the negative electrode film layer in the first direction is less than or equal to 100 mm. In some embodiments, the size of the negative electrode film layer in the first direction is 70 mm to 100 mm. In this way, the negative electrode film layer near the side close to the negative electrode tab and the side far from the negative electrode tab can be caused to be more uniformly intercalated with lithium, further facilitating improvement in lithium precipitation, thereby further facilitating fast charging performance and cycle performance of the battery cell.

[0010] In some embodiments, the electrode assembly comprises a stack structure and / or a wound structure.

[0011] In some embodiments, the electrode assembly comprises a wound structure, and in the electrode assembly of the wound structure, each layer of the negative electrode tab, except for the outermost negative electrode tab, comprises the negative electrode tab extending in the first direction. In this way, the number of negative electrode tabs in the electrode assembly reaches a maximum, so that there are more negative electrode tabs to shunt, and the current density on each negative electrode tab is smaller, which is more conducive to reducing the intercalation reaction rate per unit negative electrode film layer, thereby more conducive to improving the problem of increased intercalation overpotential of the negative electrode on the tab side, and further more conducive to improving lithium precipitation.

[0012] In some embodiments, the thickness of the negative electrode film layer on a single side is less than or equal to 80 μm in a full discharge state. In some embodiments, the thickness of the negative electrode film layer on a single side is 47 μm to 75 μm in a full discharge state. In this way, it is conducive to further improving the fast charging performance.

[0013] In some embodiments, the single-sided coating weight of the negative electrode film layer is 100 mg / 1540.25 mm 2 to 160 mg / 1540.25 mm 2 . In this way, it is conducive to uniform deintercalation of lithium ions in the thickness direction of the negative electrode tab, thereby facilitating improvement in the kinetic performance of the battery cell, and further facilitating improvement in the fast charging performance.

[0014] In some embodiments, the compaction density of the negative electrode tab is 1.3 g / cm 3 to 1.75 g / cm 3 . In this way, the fast charging performance and energy density of the battery cell can be balanced.

[0015] In some embodiments, the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a graphite material, and the volume distribution particle size Dv50 of the graphite material is 7 μm to 22 μm. In this way, the graphite material with smaller particle size has more active sites per unit area, which is conducive to improving the intercalation kinetics, thereby facilitating improvement in the fast charging performance of the battery cell.

[0016] In some embodiments, the specific surface area of the graphite material is 0.8 cm 2 / g to 2.5 cm 2 / g. In this way, the specific surface area of the graphite material is small, and the active sites in contact with the electrolyte are less, which can reduce the side reactions in the cycle period, and is conducive to improving the cycle performance and fast charging performance of the battery cell.

[0017] In some embodiments, the OI value of the negative electrode tab is 8-14; wherein the OI value of the negative electrode tab is the ratio of the diffraction peak area of the (003) crystal plane to the (110) crystal plane corresponding to the negative electrode active material in the XRD diffraction spectrum of the negative electrode tab. In this way, the fast charging performance and cycle performance of the secondary battery can be further improved.

[0018] In some embodiments, the porosity of the negative electrode tab is 23%-36%. In this way, it is conducive to further improving the fast charging performance of the battery cell.

[0019] In some embodiments, the electrode assembly further comprises a positive electrode tab, the positive electrode tab comprising a positive electrode current collector and a positive electrode film layer, the positive electrode current collector comprising a positive electrode current collecting portion and a positive electrode tab extending from the positive electrode current collecting portion in the first direction; the positive electrode film layer is located on at least one side of the positive electrode current collecting portion; the size w3 of the positive electrode tab in the second direction and the size w2 of the electrode assembly in the second direction satisfy: 15%≤w3 / w2≤30%. In some embodiments, the size w3 of the positive electrode tab in the second direction and the size w2 of the electrode assembly in the second direction satisfy: 17%≤w3 / w2≤28%. In this way, the width of the positive electrode tab is wide and within a suitable range, which can optimize the current distribution density on the positive electrode tab on the basis of meeting the processing requirements and safety performance, so that the current density on the positive electrode tab is reduced. The reduction of the current density on the positive electrode tab is conducive to reducing the heat generation on the positive electrode tab side, thereby on the one hand, the side reaction between the positive electrode and the electrolyte can be reduced, and the stability of the positive electrode film layer can be improved, on the other hand, the loss of active sites of the positive electrode active material at high state of charge can be reduced, thereby being conducive to further improving the cycle performance of the battery cell.

[0020] In some embodiments, the size w3 of the positive electrode tab in the second direction is 30 mm to 60 mm. In this way, on the one hand, the current density of the tab per unit area can be reduced, thereby being conducive to reducing the heat generation on the positive electrode tab side, and thereby improving the cycle performance of the battery cell; on the other hand, it will not affect the subsequent welding process and will not be lapped with the negative electrode tab, which is further conducive to the processing performance and safety performance of the battery cell.

[0021] In some embodiments, the electrode assembly comprises a wound structure electrode assembly, in which each layer of the positive electrode tab comprises the positive electrode lug extending in the first direction. In this way, the number of positive electrode lugs in the electrode assembly is maximized, so that there are more positive electrode lugs to shunt, and the current density on each positive electrode lug is smaller, which is more conducive to reducing the heat generation on the positive electrode lug side, thereby more conducive to improving the cycle performance of the battery cell.

[0022] In some embodiments, the positive electrode film layer has a size L2 in the first direction of less than or equal to 98 mm. In this way, the positive electrode film layer near the negative-positive electrode lug side and the positive electrode lug side is more uniformly delithiated, which is further conducive to improving the deintercalation rate of lithium ions, thereby improving lithium precipitation.

[0023] In some embodiments, the thickness of the single-sided positive electrode film layer is 58 μm to 93 μm. In this way, it is conducive to balancing the energy density and fast charging performance of the battery cell.

[0024] In some embodiments, the single-sided coating weight of the positive electrode film layer is 220 mg / 1540.25 mm 2 to 350 mg / 1540.25 mm 2 . In this way, it is conducive to further improving the energy density and fast charging performance of the battery cell.

[0025] In some embodiments, the compaction density of the positive electrode tab is 2.4 g / cm 3 to 2.75 g / cm 3 . In this way, it is conducive to further balancing the energy density and fast charging performance of the battery cell.

[0026] In some embodiments, the positive electrode film layer comprises a positive electrode active material, and the positive electrode active material comprises a lithium-containing phosphate with an olivine structure. In this way, it is further conducive to improving the fast charging performance and cycle stability of the battery cell.

[0027] In some embodiments, the positive electrode active material comprises one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate, and a modified substance of any of the foregoing.

[0028] In some embodiments, the positive electrode active material comprises a modification element, and the modification element comprises one or more of Al, V, Ti, Zr, Hf, Ge, and Sn. In this way, it is conducive to further improving the cycle performance and energy density of the battery cell.

[0029] In some embodiments, the modification element comprises Al, V, and Ti. In this way, it is conducive to balancing the cycle performance and energy density of the battery cell.

[0030] In some embodiments, the mass percentage of the modifying element in the positive electrode active material is 100 ppm-5000 ppm.

[0031] In some embodiments, the negative electrode tab further comprises a negative electrode conductive layer, the negative electrode conductive layer being located between the negative electrode current collector and the negative electrode film layer; and / or, the positive electrode tab further comprises a positive electrode conductive layer, the positive electrode conductive layer being located between the positive electrode current collector and the positive electrode film layer. Thereby, it is beneficial to further improve the fast charging performance of the battery cell.

[0032] In some embodiments, the thickness of the negative electrode conductive layer is 0.1-5 μm; and / or, the thickness of the positive electrode conductive layer is 0.1-5 μm. Thereby, it is beneficial to further improve the fast charging performance of the battery cell.

[0033] In some embodiments, further comprising an electrolyte, the electrolyte comprising a lithium-containing electrolyte salt; the lithium-containing electrolyte salt comprising one or more of a fluorine-containing sulfonimide salt and lithium hexafluorophosphate. Thereby, it is more beneficial to improve the cycle performance and fast charging performance of the battery cell.

[0034] In some embodiments, the mass percentage of the lithium-containing electrolyte salt is 10%-20% based on the total mass of the electrolyte. Thereby, it is possible to further balance the fast charging performance and cycle stability of the battery cell.

[0035] In some embodiments, the lithium-containing electrolyte salt comprises a fluorine-containing sulfonimide salt and lithium hexafluorophosphate; the mass ratio of the fluorine-containing sulfonimide salt and the lithium hexafluorophosphate is (1:4)-(4:1) based on the total mass of the lithium-containing electrolyte salt. Thereby, it is beneficial to further improve the fast charging performance and cycle performance of the battery cell.

[0036] In some embodiments, the electrolyte comprises a solvent, the solvent comprising a carboxylic acid ester-based solvent and / or a carbonate-based solvent. Thereby, it is beneficial to further comprehensively improve the fast charging performance and cycle stability under fast charging of the battery cell.

[0037] In some embodiments, the mass percentage of the solvent is 73%-89.95% based on the total mass of the electrolyte. Thereby, the electrolyte has good electrical conductivity and stability, which is beneficial to further improve the fast charging performance and cycle performance of the battery cell.

[0038] In some embodiments, the lithium-containing electrolyte salt comprises a carboxylic ester solvent and a carbonate solvent; the mass ratio of the carboxylic ester solvent and the carbonate solvent is (1:6) to (1:1) based on the total mass of the solvent. In this way, the electrolyte has good electrical conductivity, stability and appropriate viscosity, thereby further improving the fast-charging performance and cycle performance of the battery cell.

[0039] In some embodiments, the electrolyte comprises an additive, the additive comprising one or more of a lithium salt additive, a carbonate additive, a sulfur-containing additive. In this way, the fast-charging performance and cycle stability of the battery cell are further improved.

[0040] In some embodiments, the mass fraction of the additive is 0.1% to 7% based on the total mass of the electrolyte. In this way, the cycle stability and fast-charging performance of the battery cell are further improved.

[0041] In some embodiments, the additive comprises a lithium salt additive; the mass fraction of the lithium salt additive is 0.1% to 3% based on the total mass of the electrolyte. In this way, the fast-charging performance and cycle stability of the battery cell are further improved.

[0042] In some embodiments, the lithium salt additive comprises one or more of lithium difluorophosphate, lithium difluoro oxalate borate, lithium tetrafluoroborate, lithium bisoxalate borate.

[0043] In some embodiments, the lithium salt additive comprises lithium difluoro oxalate borate; the mass fraction of the lithium difluoro oxalate borate is 0.1%-1.5% based on the total mass of the electrolyte. In this way, the stability of the SEI film and the viscosity of the electrolyte are balanced, thereby further improving the cycle life and fast-charging performance of the battery cell.

[0044] In some embodiments, the electrical conductivity of the electrolyte is 10 mS / cm to 20 mS / cm. In this way, the fast-charging performance and cycle performance of the battery cell are further improved.

[0045] In some embodiments, the electrode assembly further comprises a separator film, the separator film comprising a base film and a coating layer disposed on at least one side of the base film; the coating layer comprises a ceramic coating layer and an aqueous adhesive layer, the ceramic coating layer being disposed between the base film and the aqueous adhesive layer. In this way, the risk of lithium precipitation during cycling is reduced, thereby further improving the fast-charging performance and cycle performance of the battery cell.

[0046] In some embodiments, the ceramic coating comprises a ceramic material comprising one or more of alumina, boehmite, silica, magnesia, titania, tin oxide, calcium oxide, zirconia, yttria, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

[0047] In some embodiments, the aqueous bonding layer comprises a bonding material comprising one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer.

[0048] In some embodiments, the base film has a thickness of 5-10 μm; and / or, the coating has a thickness of 0.5-3 μm. Thereby, the safety performance and energy density of the battery cell are further balanced.

[0049] In some embodiments, the separator film has a porosity of 20-60%. Thereby, the energy density, fast charging performance, and cycle stability of the battery cell are further balanced.

[0050] In some embodiments, the battery cell comprises a housing and a cover plate assembly disposed at at least one end of the housing, the housing and the cover plate assembly defining a receiving cavity, the electrode assembly being disposed in the receiving cavity, and the housing wall thickness of the large surface of the battery cell is 0.4-0.65 mm. Thereby, the energy density of the battery cell is further improved.

[0051] In some embodiments, the cover plate assembly comprises a cover plate, a first electrode terminal, and a second electrode terminal, the first electrode terminal and the second electrode terminal having opposite polarities; the minimum cross-sectional area S of the first electrode terminal and / or the second electrode terminal satisfies: 600 mm 2 ≤ S ≤ 1100 mm 2 . Thereby, the overcurrent capacity of the battery cell is improved, the heat generation of the electrode terminal is reduced, the internal resistance of the battery cell is reduced, and the fast charging performance and cycle stability of the battery cell are improved.

[0052] In some embodiments, the volume ratio of the electrode assembly in the receiving cavity is 75-90%. In some embodiments, the volume ratio of the electrode assembly in the receiving cavity is 80-88%. Thereby, on the one hand, the volume energy density of the battery cell is improved, and on the other hand, there is enough space for liquid injection in the receiving cavity, which is conducive to the improvement of the fast charging performance, cycle performance, and safety performance of the battery cell.

[0053] The second aspect of the present application provides a battery device comprising the battery cell provided in the first aspect.

[0054] The third aspect of the present application provides a power consumption device comprising the battery device provided in the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 is a structural schematic diagram of an electrode assembly of a winding structure of an embodiment of the present application.

[0056] Figure 2 is a structural schematic diagram of a negative electrode tab in the electrode assembly of Figure 1 .

[0057] Figure 3 is a structural schematic diagram of a positive electrode tab in the electrode assembly of Figure 1 .

[0058] Figure 4 is a cross-sectional structural schematic diagram of a separator film of an embodiment of the present application.

[0059] Figure 5 is a schematic diagram of a battery monomer of an embodiment of the present application.

[0060] Figure 6 is an exploded view of the battery monomer of an embodiment of the present application shown in Figure 5 .

[0061] Figure 7 is a schematic diagram of a battery module of an embodiment of the present application.

[0062] Figure 8 is a schematic diagram of a battery pack of an embodiment of the present application.

[0063] Figure 9 is an exploded view of the battery pack of an embodiment of the present application shown in Figure 8 .

[0064] Figure 10 is a schematic diagram of a power consumption device using the battery monomer as a power supply of an embodiment of the present application.

[0065] BRIEF DESCRIPTION OF DRAWINGS

[0066] 100 electrode assembly; 10 negative electrode tab; 101 negative electrode current collecting part; 102 negative electrode tab; 20 positive electrode tab; 201 positive electrode current collecting part; 202 positive electrode tab; 30 separator film; 301 base film; 302 coating layer; 3021 ceramic coating layer; 3022 water-based adhesive layer; 1 battery pack; 2 upper box body; 3 lower box body; 4 battery module; 5 battery monomer; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0067] Hereinafter, embodiments of the battery cell, the battery device, and the electric device of the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known to those skilled in the art, repeated description of substantially identical configurations, is omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to define the subject matter of the claims.

[0068] In the present application, unless otherwise specified, a numerical range "a-b" represents a shorthand for indicating any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been all listed herein, and "0-5" is just a shorthand for indicating these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like.

[0069] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0070] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0071] Unless otherwise specified, all steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), and the like.

[0072] Unless otherwise specified, the terms used in the present application have the commonly understood meanings understood by those skilled in the art.

[0073] Unless otherwise specified, the values of the parameters mentioned in the present application can be measured by various test methods commonly used in the art, for example, can be measured according to the test methods given in the present application.

[0074] Currently, during the charging process of the battery cell, the negative current density on the tab side is large, which leads to an increase in the negative electrode lithium intercalation overpotential on the tab side, and easily causes lithium precipitation. Lithium precipitation in the battery cell will on the one hand deteriorate the lithium intercalation kinetics and affect the fast charging performance of the battery, and on the other hand, the precipitated metal lithium will react with the electrolyte, which will increase the heat generation and further increase the gas generation of the battery cell, and deteriorate the cycle life of the battery cell.

[0075] In order to solve the problem of lithium precipitation in the battery cell, the related art reduces the coating weight and the compaction density of the pole piece, but this will reduce the energy density of the battery cell.

[0076] Based on this, the present application provides a new battery cell, a battery device and a power utilization device. The battery cell in the present application has excellent fast charging performance and cycle performance. The present application and optional embodiments are described in more detail below.

[0077] Battery cell

[0078] The first aspect of the present application provides a battery cell, comprising an electrode assembly, the electrode assembly comprising a negative pole piece and a positive pole piece; the negative pole piece comprising a negative current collector and a negative film layer, the negative current collector comprising a negative current collecting part and a negative tab extending from the negative current collecting part in a first direction; the negative film layer is located on at least one side of the negative current collecting part; the size w1 of the negative tab in the second direction and the size w2 of the electrode assembly in the second direction satisfy: 15%≤w1 / w2≤30%; the first direction is the width direction of the negative pole piece, and the second direction is the length direction of the negative pole piece.

[0079] The application satisfies the processing requirements and safety performance, optimizes the current distribution density on the negative electrode tab, and reduces the current density on the negative electrode tab by limiting the size w1 of the negative electrode tab in the second direction and the size w2 of the electrode assembly in the second direction to satisfy the above condition, so that the width of the negative electrode tab is wider and within a suitable range. Specifically, the current density = current / conductive area. For the same size of current, when the width of the negative electrode tab is wider, the area of the negative electrode tab is larger, and then the current density per unit area on the negative electrode tab will decrease. The reduction of the current density on the negative electrode tab reduces the current density flowing into the negative electrode current collector, and correspondingly, the current density transmitted into the negative electrode film layer is reduced, so the current per unit area on the negative electrode film layer is smaller, thereby facilitating the reduction of the lithium intercalation reaction rate per unit area of the negative electrode film layer. The reduction of the lithium intercalation reaction rate reduces the activation energy barrier requirement of the lithium ion passing through the electrode or electrolyte interface, reduces the activation overpotential, and on the other hand, the diffusion rate of the lithium ion meets the reaction requirement, and the concentration difference overpotential is reduced. Therefore, the current density per unit area on the negative electrode film layer is smaller, which can reduce the overpotential of the negative electrode lithium intercalation on the tab side, thereby improving the lithium precipitation. The improvement of lithium precipitation, on the one hand, is conducive to improving the lithium intercalation kinetics, thereby improving the fast charging performance of the battery monomer, and on the other hand, can reduce the probability of side reactions with electrolyte, thereby reducing heat generation, and is conducive to improving the cycle life of the battery monomer. In addition, the reduction of the current density on the tab can also improve the heat generation at the tab, thereby reducing the probability of side reactions at the tab, and further facilitating the cycle performance of the battery monomer.

[0080] In some embodiments, the electrode assembly comprises a stack structure and / or a winding structure; optionally, the electrode assembly comprises a winding structure.

[0081] The stack structure refers to an electrode assembly formed by alternately stacking negative electrode tabs, isolation films, positive electrode tabs, and isolation films. The winding structure refers to an electrode assembly formed by winding a negative electrode tab, an isolation film, and a positive electrode tab along a winding axis through multiple bending.

[0082] In some embodiments, one electrode assembly can comprise one or more winding cores of the stack structure, wherein the plurality of winding cores are connected in parallel. As an example, one electrode assembly can comprise two winding cores of the stack structure connected in parallel.

[0083] In some embodiments, one electrode assembly can comprise one or more winding cores of the winding structure, wherein the plurality of winding cores are connected in parallel. As an example, one electrode assembly can comprise two winding cores of the winding structure connected in parallel.

[0084] In some embodiments, one electrode assembly can comprise winding cores of the stack structure and winding cores of the winding structure connected in parallel to each other.

[0085] It should be noted that for the electrode assembly of the stack structure, the size of the electrode assembly in the second direction is generally slightly larger than the size of the negative electrode tab in the second direction, or can be understood as the size of the single layer of the separator film in the second direction. For the electrode assembly of the winding structure, the size of the electrode assembly in the second direction refers to the maximum outer diameter size of the winding body in the second direction.

[0086] Exemplarily, the size w1 of the negative electrode tab in the second direction and the size w2 of the electrode assembly in the second direction satisfy w1 / w2 is 15%, 16%, 16.5%, 17%, 17.5%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 26.5%, 27%, 27.5%, 28%, 29%, 30% or a range between any two of them. In some embodiments, the size w1 of the negative electrode tab in the second direction and the size w2 of the electrode assembly in the second direction satisfy: 17%≤w1 / w2≤28%. Thus, it is more beneficial to optimize the current distribution density on the negative electrode tab on the basis of meeting the processing requirements and safety performance, so that the current density on the tab is reduced, thereby more beneficial to reduce the overpotential of lithium intercalation on the tab side of the negative electrode, thereby further improving lithium precipitation, and further beneficial to the fast charging performance and cycle performance of the battery cell.

[0087] In the following, taking the electrode assembly of the winding structure as an example, the scheme of the present application is explained in combination with Figures 1 to 3

[0088] Figure 1 FIG. 1 is a structural schematic diagram of the electrode assembly of the winding structure according to an embodiment of the present application, Figure 2 Figure 1 FIG. 2 is an unfolded structural schematic diagram of the negative electrode tab in the electrode assembly of the winding structure, and Figure 1 2 As shown in FIG. 2, the electrode assembly 100 of the winding structure includes a negative electrode tab 10, a positive electrode tab 20 and a separator film 30. The negative electrode tab 10 includes a negative electrode current collector and a negative electrode film layer (not shown). The negative electrode current collector includes a negative electrode current collecting portion 101 and a negative electrode tab 102 extending from the negative electrode current collecting portion in the first direction. The negative electrode film layer is located at least one side of the negative electrode current collecting portion 101. The size w1 of the negative electrode tab 102 in the second direction and the size w2 of the electrode assembly 100 in the second direction satisfy: 15%≤w1 / w2≤30%. In the present application, the size w1 of the negative electrode tab 102 in the second direction and the size w2 of the electrode assembly 100 in the second direction can be measured by a ruler.

[0089] It should be noted that in order to facilitate understanding of the specific structure of the electrode assembly of the winding structure and the position of the negative electrode tab, Figure 1 Figure 2 ​​​​Two negative tabs 102 are merely exemplarily shown, and in practice, the negative tab sheet can contain more negative tabs. In addition, Figure 2 An expanded view of the negative tab sheet is shown merely for the purpose of facilitating the understanding of the positional relationship between the negative current collector and the negative tab, Figure 2 The position of the negative tab does not completely correspond to Figure 1 The position of the negative tab does not completely correspond to

[0090] In some embodiments, the size w1 of the negative tab in the second direction is 30-60 mm. Optionally, the size w1 of the negative tab in the second direction is 35-55 mm. The size of the negative tab in the second direction within the above range, on the one hand, can reduce the current density of the unit area tab, thereby facilitating the reduction of the lithium intercalation reaction rate in the unit area negative film layer, thereby improving lithium precipitation, and further facilitating the fast charging performance and cycle performance of the battery cell; on the other hand, it will not affect the subsequent welding process and will not be overlapped with the positive tab, further facilitating the processing performance and safety performance of the battery cell.

[0091] Exemplarily, the size w1 of the negative tab in the second direction is 30 mm, 32 mm, 35 mm, 38 mm, 40 mm, 42 mm, 45 mm, 48 mm, 50 mm, 52 mm, 55 mm, 58 mm, 60 mm, or a value between any two of them.

[0092] In some embodiments, please continue to refer to Figure 2 The negative film layer (not shown) is located on at least one side of the negative current collector 101, and the size L1 of the negative film layer in the first direction is less than or equal to 100 mm. Optionally, the size L1 of the negative film layer in the first direction is 70-100 mm. Since the size L1 of the negative film layer in the first direction is less than or equal to 100 mm, it indicates that the width of the negative film layer of the battery cell of the present application is small, so that when the current passes through the negative tab in the first direction during charging, there will be no large potential difference between the negative film layer close to the negative tab side and the negative film layer away from the negative tab side, thereby making the negative film layer close to the negative tab side and the negative film layer away from the negative tab side intercalate lithium more uniformly, further facilitating the improvement of lithium precipitation, thereby further facilitating the fast charging performance and cycle performance of the battery cell.

[0093] Exemplarily, the size L1 of the negative film layer in the first direction is 70 mm, 72 mm, 74 mm, 75 mm, 76 mm, 78 mm, 80 mm, 82 mm, 85 mm, 88 mm, 90 mm, 92 mm, 94 mm, 95 mm, 98 mm, 100 mm, or a value between any two of them.

[0094] In the present application, the size L1 of the negative electrode film layer along the first direction can be obtained by disassembling the battery monomer, obtaining the negative electrode tab, and then measuring with a ruler.

[0095] In some embodiments, for the electrode assembly of the stack structure, each negative electrode tab includes a negative electrode tab along the first direction extending from the negative electrode current collector. After the stack forms the electrode assembly, a plurality of negative electrode tabs are sequentially stacked to form a negative electrode tab group, and the projections of the plurality of negative electrode tabs coincide or substantially coincide along the stacking direction of the negative electrode tab. Here, “substantially coincide” means that due to process reasons, there may be a slight misalignment between adjacent negative electrode tabs.

[0096] In some embodiments, for the electrode assembly of the winding structure, the negative electrode current collector can include a plurality of negative electrode tabs extending from the negative electrode current collector along the first direction; optionally, after forming the electrode assembly, each circle of negative electrode tabs contains one negative electrode tab, i.e., one circle of negative electrode tabs contains one negative electrode tab, except for the outermost circle.

[0097] Since the negative electrode tab includes a plurality of negative electrode tabs, during the charging process, the current can be shunted through the plurality of negative electrode tabs, thereby reducing the current density on each negative electrode tab, further reducing the current density per unit area of the negative electrode film layer, thereby facilitating further reduction of the lithium intercalation reaction rate per unit negative electrode film layer. The reduction of the lithium intercalation reaction rate reduces the activation energy barrier requirement for the charge transfer of lithium ions through the electrode or electrolyte interface, reduces the activation overpotential, and increases the diffusion rate of lithium ions to meet the reaction requirements, thereby reducing the concentration overpotential. Therefore, the problem of increased lithium intercalation overpotential on the negative electrode tab side can be further improved, thereby further improving the lithium precipitation, and further improving the fast charging performance and cycle performance of the battery monomer.

[0098] In some embodiments, for the electrode assembly of the winding structure, after winding to form the electrode assembly, a plurality of negative electrode tabs are sequentially stacked to form a negative electrode tab group, and the projections of the plurality of negative electrode tabs coincide or substantially coincide along the stacking direction of the negative electrode tab. Here, “substantially coincide” means that due to process reasons, there may be a slight misalignment between adjacent negative electrode tabs.

[0099] In some embodiments, the electrode assembly includes a winding structure, and in the electrode assembly of the winding structure, each layer of negative electrode tabs includes a negative electrode tab extending along the first direction, except for the negative electrode tab of the outermost circle. Thus, the number of negative electrode tabs in the electrode assembly is maximized, so that more negative electrode tabs can be used for shunting, and the current density on each negative electrode tab is smaller, which is more conducive to reducing the lithium intercalation reaction rate per unit negative electrode film layer, thereby more effectively improving the problem of increased lithium intercalation overpotential on the negative electrode tab side, and further improving the lithium precipitation.

[0100] In this document, the term "each layer of negative electrode tab including negative electrode tab tab includes negative electrode tab" refers to: in the wound electrode assembly, each layer contains two negative electrode tabs, and the projections of the two negative electrode tabs are coincident or substantially coincident in the stacking direction of the negative electrode tab. For the outermost layer of negative electrode tab, it may contain one negative electrode tab or no negative electrode tab, which is designed according to the position of the end of the negative electrode tab and other conditions.

[0101] In some embodiments, the thickness of the single-sided negative electrode film layer is less than or equal to 80 μm in the full discharge state. Optionally, the thickness of the single-sided negative electrode film layer is 47 μm to 75 μm. In the full discharge state, the thickness of the single-sided negative electrode film layer is within the above range, which means that the thickness of the negative electrode film layer in this application is small, so the impedance of lithium ion diffusion into the negative electrode tab is low, which is beneficial to the uniform deintercalation of lithium in the thickness direction of the negative electrode tab, thereby improving the kinetic performance of the battery monomer, and further improving the fast charging performance.

[0102] Exemplarily, the thickness of the single-sided negative electrode film layer is 47 mm, 50 mm, 52 mm, 55 mm, 57 mm, 59 mm, 60 mm, 63 mm, 64 mm, 66 mm, 68 mm, 70 mm, 72 mm, 74 mm, 75 mm, 76 mm, 78 mm, 80 mm or a value between any two of them.

[0103] In this document, the term "full discharge state" refers to the state in which the battery monomer is discharged completely and the remaining capacity (State of Charge, SOC) is close to zero or reaches the theoretical minimum value.

[0104] In this application, the thickness of the single-sided negative electrode film layer can be measured by disassembling the battery monomer, obtaining the negative electrode tab, and then using instruments and methods known in the art. Assuming that the negative electrode tab to be measured is a double-sided coated negative electrode tab, first measure the thickness of the negative electrode tab at at least 12 different positions in the thickness direction of the negative electrode tab using a micrometer (e.g. Mitutoyo 293-100, accuracy 0.1 μm), then take the average value as the thickness of the negative electrode tab, then wipe off the negative electrode film layer on both sides, and then measure the thickness of the negative electrode current collector in the same way, the thickness of the single-sided negative electrode film layer = (thickness of the negative electrode tab - thickness of the negative electrode current collector) / 2.

[0105] In some embodiments, the single-sided coating weight of the negative electrode film layer is 100 mg / 1540.25 mm 2 to 160 mg / 1540.25 mm 2 ; optionally, the single-sided coating weight of the negative electrode film layer is 125 mg / 1540.25 mm 2 to 145 mg / 1540.25 mm2 The single-side coating weight of the negative electrode film layer in the above range can balance the fast-charging performance and energy density of the battery cell. Illustratively, the single-side coating weight of the negative electrode film layer is 100 mg / 1540.25 mm 2 , 110 mg / 1540.25 mm 2 , 120 mg / 1540.25 mm 2 , 125 mg / 1540.25 mm 2 , 130 mg / 1540.25 mm 2 , 133 mg / 1540.25 mm 2 , 140 mg / 1540.25 mm 2 , 145 mg / 1540.25 mm 2 , 150 mg / 1540.25 mm 2 , 160 mg / 1540.25 mm 2 , or a value between any two of the above values.

[0106] In the present application, the single-side coating weight of the negative electrode film layer refers to the weight of the negative electrode film layer per unit area on the side of the negative electrode current collector.

[0107] In the present application, the single-side coating weight of the negative electrode film layer can be tested by methods known in the art. For example, the negative electrode sheet can be obtained from a disassembled battery cell (if it is a double-sided coated negative electrode sheet, the negative electrode active material layer on one side can be wiped off first), punched into a small round piece with an area of S1, weighed, and recorded as M1. Then the negative electrode film layer of the above weighed negative electrode sheet is wiped off, and the mass of the negative electrode current collector is weighed and recorded as M0. The single-side coating weight of the negative electrode film layer = (M1-M0) / S1.

[0108] In some embodiments, the compaction density of the negative electrode sheet is 1.3 g / cm 3 to 1.75 g / cm 3 ; optionally, the compaction density of the negative electrode sheet is 1.35 g / cm 3 to 1.5 g / cm 3 . The compaction density of the negative electrode sheet in the above range indicates that the negative electrode film layer has a larger porosity, which can provide a more unobstructed channel for the transport of lithium ions, can quickly improve the de-intercalation kinetics of lithium ions, and reduce the risk of lithium precipitation in the battery cell, thereby being conducive to improving the safety performance and cycle life of the battery cell.

[0109] Illustratively, the compaction density of the negative electrode sheet is 1.3 g / cm 3 , 1.35 g / cm 3 , 1.4 g / cm 3 , 1.43 g / cm3 1.45 g / cm3 3 1.5 g / cm3 3 1.6 g / cm3 3 1.65 g / cm3 3 1.7 g / cm3 3 1.75 g / cm3 3 or a value between any two of the above-mentioned values.

[0110] In the present application, the compaction density of the negative electrode tab is the meaning known in the art, which can be measured by instruments and methods known in the art. The compaction density of the negative electrode tab = the area density of the negative electrode film layer / the thickness of the negative electrode film layer. The thickness of the negative electrode film layer can be measured by instruments and methods known in the art, for example, a micrometer (e.g., Mitutoyo 293-100, accuracy 0.1 μm) can be used to measure the thickness of the negative electrode tab at at least 12 different positions along the thickness direction of the negative electrode tab, and then the average value is taken as the thickness of the negative electrode tab, and then the thickness of the negative electrode current collector is subtracted to obtain the thickness of the negative electrode film layer. The area density of the negative electrode film layer can be measured by instruments and methods known in the art, for example, the negative electrode tab after cold pressing or the negative electrode tab obtained after battery disassembly (if it is a double-sided coated negative electrode tab, the negative electrode film layer on one side is wiped off first), is punched into a small disc with an area of S1, and its weight is measured and recorded as M1. Then the negative electrode film layer of the above-weighed negative electrode tab is wiped off, and the weight of the negative electrode current collector is measured and recorded as M0. The area density of the negative electrode film layer = (M1-M0) / S1.

[0111] In some embodiments, the negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a graphite material, and the volume distribution particle size Dv50 of the graphite material is 7 μm to 22 μm; optionally, the volume distribution particle size Dv50 of the graphite material is 9 μm to 15 μm. The volume distribution particle size Dv50 of the graphite material in the above range reflects that the particle size of the graphite material is small, and the active sites per unit area of the graphite material with small particle size are more, which is beneficial to improve the lithium intercalation kinetics, thereby being beneficial to improve the fast charging performance of the battery monomer.

[0112] Illustratively, the volume distribution particle size Dv50 of the graphite material is 7 μm, 8 μm, 9 μm, 10 μm, 10.2 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, or a value between any two of the above-mentioned values.

[0113] In the present application, the volume distribution particle size Dv50 of the graphite material is the particle size corresponding to the cumulative volume distribution percentage of the graphite material reaching 50%, which can be measured by instruments and methods known in the art. For example, the laser particle size analyzer can be used for measurement according to the standard GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK. Specifically, the battery monomer can be disassembled to obtain the negative electrode sheet, and then the powder of the negative electrode sheet can be scraped for the above laser particle size analysis test.

[0114] In some embodiments, the specific surface area of the graphite material is 0.8 cm 2 / g to 2.5 cm 2 / g; optionally, the specific surface area of the graphite material is 0.9 cm 2 / g to 1.3 cm 2 / g. In this way, the specific surface area of the graphite material is small, and the active sites in contact with the electrolyte are less, which can reduce the side reactions in the cycle period, and is beneficial to improve the cycle performance and fast charging performance of the battery monomer.

[0115] Illustratively, the specific surface area of the graphite material is 0.8 cm 2 / g, 1.0 cm 2 / g, 1.1 cm 2 / g, 1.2 cm 2 / g, 1.5 cm 2 / g, 1.8 cm 2 / g, 2.0 cm 2 / g, 2.2 cm 2 / g, 2.5 cm 2 / g or a range between any two of them.

[0116] In the present application, the specific surface area has the meaning known in the art, which can be tested by instruments or methods known in the art. Specifically, the battery monomer can be disassembled to obtain the negative electrode sheet, and then the powder of the negative electrode film layer can be scraped as the sample to be tested, and then the specific surface area of the sample to be tested can be tested by gas adsorption method, specifically according to the standard test of GB / T 19587-2017, and calculated by BET (Brunauer Emmett Teller) method. The testing instrument can be a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Corporation, USA.

[0117] In some embodiments, the OI value of the negative electrode tab is 8-14; optionally, the OI value of the negative electrode tab is 10-13. Illustratively, the OI value of the negative electrode tab is 8, 8.3, 9, 10, 11, 11.4, 11.65, 11.7, 12, 13, 13.8, 14, or a value between any two of them.

[0118] In the present application, the OI value of the negative electrode tab refers to the ratio of the diffraction peak intensity of the 004 crystal plane of the graphite material in the negative active material layer to the diffraction peak intensity of the 110 crystal plane, which can be used to characterize the orientation of the negative active material layer and reflect the anisotropy degree of the grain arrangement in the negative active material layer. The 004 crystal plane corresponds to the graphite with the layer structure parallel to the tab, and the 110 crystal plane corresponds to the graphite with the layer structure perpendicular to the tab; the higher the OI value, the higher the crystal orientation degree, and the more limited the surface of the active ion on the active material in the tab. The lower the OI value, the lower the crystal orientation degree, and the active ion can be deintercalated from multiple directions on the active material in the tab. By limiting the OI value of the negative electrode tab within the above range, the active ion can be quickly deintercalated in the negative electrode tab, which can further improve the fast charging performance of the secondary battery. In addition, when the OI value of the negative electrode tab is within the above range, the expansion between the graphite layers can also be inhibited, ensuring the high stability of the material structure during the cycle process and further improving the cycle performance of the battery monomer.

[0119] In the present application, the OI value of the negative electrode tab has the meaning known in the art, which can be tested by the intensity of the 004 crystal plane diffraction peak and the 110 crystal plane diffraction peak through an X-ray powder diffractometer (non-limiting example X'pert PRO), obtained from the X-ray diffraction spectrum according to the general method of X-ray diffraction analysis and the determination method of graphite lattice parameters JIS K 0131-1996, JB / T4220-2011, and then according to OI = I 004 / I 110 to obtain the intensity ratio of the 004 crystal plane diffraction peak and the 110 crystal plane diffraction peak of the negative active material layer, wherein I 004 is the intensity of the 004 crystal plane diffraction peak, and I 110 is the intensity of the 110 crystal plane diffraction peak.

[0120] In some embodiments, the porosity of the negative electrode tab is 23%-36%; optionally, the porosity of the negative electrode tab is 25%-31%. The porosity of the negative electrode tab within the above range is beneficial to improve the tortuosity of the negative electrode tab and reduce the lithium ion transmission path, thereby further improving the fast charging performance of the battery monomer.

[0121] Exemplarily, the porosity of the negative electrode tab is 23%, 24%, 25%, 26%, 27%, 28%, 28.3%, 28.9%, 29%, 29.6%, 30%, 31%, 32%, 32.4%, 33% or a value between any two of the above values.

[0122] In the present application, the porosity of the negative electrode tab can be tested by a method known in the art. For example, the negative electrode tab is cleaned by immersing in ethyl methyl carbonate (EMC) according to the national standard GB / T24586-2009; and the porosity is determined by a gas displacement method using a test instrument, AccuPyc II 1340 (USA). The porosity of the negative electrode tab is the percentage of the pore volume in the total volume of the negative electrode tab, and the calculation formula is: porosity = (V-V0) / V x 100%, wherein V0 is the true volume of the negative electrode tab, and V is the apparent volume of the negative electrode tab.

[0123] In some embodiments, the negative active material can further include other carbon-based materials, which can be one or more of composite graphite particles, hard carbon, more optionally, the composite graphite particles include graphite bulk particles and a carbon coating layer coated on at least part of the surface of the graphite bulk particles, the graphite bulk particles include secondary particles, and the carbon coating layer includes amorphous carbon. In this document, "secondary particles" refer to particles formed by the aggregation of two or more primary particles. The composite graphite particles including secondary particles and the surface coating layer including amorphous carbon are beneficial for the infiltration of electrolyte and the improvement of the solid-phase transmission capacity of active ions, thereby further improving the fast-charging performance of the battery cell.

[0124] In some embodiments, the negative active material further includes a silicon-based material, which includes one or more of elemental silicon, silicon-carbon material, silicon-oxygen material, silicon-nitrogen material, and silicon alloy. Optionally, the silicon-based material includes one or more of silicon-carbon material, silicon-oxygen material, and silicon-nitrogen material. In this way, the energy density of the battery cell is improved.

[0125] In some embodiments, the negative current collector has two opposite surfaces in the thickness direction of the negative current collector, and the negative active material is disposed on any one or both of the two opposite surfaces of the negative current collector.

[0126] In some embodiments, the negative current collector can employ a metal foil, a foamed metal, or a composite current collector. For example, as a metal foil, silver surface-treated aluminum or stainless steel, stainless steel, copper, nickel, carbon, or titanium, etc. can be employed. The composite current collector can include a polymer material base layer and a metal layer. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, or foamed alloy, etc. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0127] In some embodiments, the negative film layer can further optionally include a binder. The binder can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0128] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0129] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as thickening agents (such as sodium carboxymethyl cellulose (CMC-Na), etc.

[0130] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0131] In some embodiments, the electrode assembly further includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive film layer, the positive current collector includes a positive current collecting portion and a positive tab extending from the positive current collecting portion along a first direction; the positive film layer is located on at least one side of the positive current collecting portion; the size w3 of the positive tab in the second direction and the size w2 of the electrode assembly in the second direction satisfy: 15%≤w3 / w2≤30%; optionally, the size w3 of the positive tab in the second direction and the size w2 of the electrode assembly in the second direction satisfy: 17%≤w3 / w2≤28%.

[0132] This application satisfies the aforementioned conditions by limiting the dimensions w3 of the positive electrode tab in the second direction to the dimensions w2 of the electrode assembly in the second direction. This results in a wider positive electrode tab within a suitable range, optimizing the current distribution density on the positive electrode tab while meeting processing requirements and safety performance. This leads to a reduction in the current density on the positive electrode tab. The reduced current density on the positive electrode tab helps reduce heat generation on the tab side, thereby reducing side reactions between the positive electrode and the electrolyte, improving the stability of the positive electrode film, and minimizing the loss of active sites in the positive electrode active material under high charge conditions. This further improves the cycle performance of the battery cell.

[0133] For example, the dimension w3 of the positive electrode tab in the second direction and the dimension w2 of the electrode assembly in the second direction satisfy a value between w3 / w2 and any two of the following values: 15%, 16%, 16.5%, 17%, 17.5%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 26.5%, 27%, 27.5%, 28%, 29%, 30%.

[0134] Figure 3 for Figure 1 A schematic diagram of the unfolded structure of the positive electrode plate in the electrode assembly, as shown below. Figure 1 and 3 As shown, the positive electrode 20 includes a positive current collector and a positive electrode film (not shown). The positive current collector includes a positive current collector portion 201 and a positive electrode tab 202 extending from the positive current collector portion 201 along a first direction. The dimension w3 of the positive electrode tab 202 along the second direction and the dimension w2 of the electrode assembly 100 along the second direction satisfy: 15% ≤ w1 / w2 ≤ 30%. In this application, the dimension w3 of the positive electrode tab 202 along the second direction and the dimension w2 of the electrode assembly 100 along the second direction can both be measured using a ruler.

[0135] It should be noted that, in order to facilitate understanding of the specific structure of the wound electrode assembly and the location of the positive electrode tab, Figure 1 and Figure 3 The two positive electrode tabs 202 are merely shown as an example; in reality, the positive electrode sheet may contain one or more positive electrode tabs. Furthermore, Figure 3 The diagram showing the unfolded state of the positive electrode plate is only for the purpose of understanding the positional relationship between the positive current collector and the positive electrode tab. Figure 3 The position of the neutral electrode tab and Figure 1 The positions of the neutral electrode tabs do not correspond perfectly.

[0136] In some embodiments, the dimension w3 of the positive electrode tab in the second direction is 30 mm to 60 mm. Optionally, the dimension w3 of the positive electrode tab in the second direction is 35 mm to 55 mm. The dimension of the positive electrode tab in the second direction within the above range, on the one hand, can reduce the current density of the unit area tab, thereby facilitating the reduction of the heat generation on the positive electrode tab side, and further improving the cycle performance of the battery cell; on the other hand, it will not affect the subsequent welding process and will not be overlapped with the negative electrode tab, further facilitating the processing performance and safety performance of the battery cell.

[0137] Illustratively, the dimension w3 of the positive electrode tab in the second direction is 30 mm, 32 mm, 35 mm, 38 mm, 40 mm, 42 mm, 45 mm, 48 mm, 50 mm, 52 mm, 55 mm, 58 mm, 60 mm, or a value between any two of them.

[0138] In some embodiments, for the electrode assembly of the stack structure, each positive electrode tab includes a positive electrode tab extending out of the positive electrode current collector in the first direction. After the stack forms the electrode assembly, a plurality of positive electrode tabs are sequentially stacked to form a positive electrode tab group, and the projections of the plurality of positive electrode tabs coincide or substantially coincide in the stacking direction of the positive electrode tab. Here, "substantially coincide" means that due to process reasons, there may be a slight misalignment between adjacent positive electrode tabs.

[0139] In some embodiments, for the electrode assembly of the winding structure, the positive electrode current collector can include a plurality of positive electrode tabs extending out of the positive electrode current collector in the first direction. Optionally, after forming the electrode assembly, each positive electrode tab contains one positive electrode tab, i.e., one positive electrode tab per circle. Since the positive electrode tab includes a plurality of positive electrode tabs, during discharging, the current can be shunted through the plurality of positive electrode tabs, thereby reducing the current density on each positive electrode tab, further reducing the heat generation on the positive electrode tab side, and further facilitating the improvement of the cycle performance of the battery cell.

[0140] In some embodiments, for the electrode assembly of the winding structure, after winding to form the electrode assembly, a plurality of positive electrode tabs are sequentially stacked to form a positive electrode tab group, and the projections of the plurality of positive electrode tabs coincide or substantially coincide in the stacking direction of the positive electrode tab.

[0141] In some embodiments, the electrode assembly includes a winding structure, and in the electrode assembly of the winding structure, each layer of positive electrode tab includes a positive electrode tab extending in the first direction. In this way, the number of positive electrode tabs in the electrode assembly reaches the maximum, so that more positive electrode tabs can be used for shunting, and the current density on each positive electrode tab is smaller, which is more conducive to reducing the heat generation on the positive electrode tab side, and thus more conducive to improving the cycle performance of the battery cell.

[0142] In this document, the phrase "each layer of the positive electrode tab includes a positive electrode tab" means that each layer of the positive electrode tab includes two positive electrode tabs, and the projections of the two positive electrode tabs are coincident or substantially coincident in the stacking direction of the positive electrode tab.

[0143] In some embodiments, please continue to refer to Figure 3 The positive electrode film layer (not shown) is located on at least one side of the positive electrode current collector 201, and the size L2 of the positive electrode film layer in the first direction is less than or equal to 98 mm; optionally, the size L2 of the positive electrode film layer in the first direction is 68 mm to 98 mm. Since the size L2 of the positive electrode film layer in the first direction is less than or equal to 98 mm, the width of the positive electrode film layer of the battery cell of the present application is small, so that when the battery cell is discharged and the current passes through the positive electrode tab in the first direction, there is no large potential difference between the positive electrode film layer close to the positive electrode tab and the positive electrode film layer away from the positive electrode tab, so that the positive electrode film layer close to the positive electrode tab and the positive electrode film layer away from the positive electrode tab can be uniformly delithiated, which is further beneficial to improve the deintercalation rate of lithium ions, thereby improving lithium precipitation.

[0144] Exemplarily, the size L2 of the positive electrode film layer in the first direction is 68 mm, 70 mm, 72 mm, 74 mm, 75 mm, 76 mm, 78 mm, 80 mm, 82 mm, 85 mm, 88 mm, 89 mm, 90 mm, 92 mm, 95 mm, 98 mm, or a value between any two of them.

[0145] In this application, the size L2 of the positive electrode film layer in the first direction can be obtained by disassembling the battery cell, obtaining the positive electrode tab, and then measuring with a ruler.

[0146] In some embodiments, the thickness of the single-sided positive electrode film layer is 58 μm-93 μm; optionally, the thickness of the single-sided positive electrode film layer is 70 μm-85 μm. Thus, it is beneficial to balance the energy density and fast charging performance of the battery cell. Exemplarily, the thickness of the single-sided positive electrode film layer is 58 μm, 60 μm, 62 μm, 65 μm, 68 μm, 70 μm, 72 μm, 75 μm, 77 μm, 78 μm, 80 μm, 82 μm, 85 μm, 88 μm, 90 μm, 93 μm, or a value between any two of them.

[0147] In the present application, the thickness of the single-sided positive electrode film layer can be measured by disassembling the battery monomer, obtaining the positive electrode tab, and then using instruments and methods known in the art. Assuming that the positive electrode tab to be measured is a double-sided coated positive electrode tab, first use a micrometer (for example, Mitutoyo 293-100, accuracy 0.1 μm) to measure the thickness of the positive electrode tab at at least 12 different positions along the thickness direction of the positive electrode tab, then take the average value as the thickness of the positive electrode tab, then wipe off the positive electrode film layer on both sides, and then measure the thickness of the negative current collector in the same way. The thickness of the single-sided positive electrode film layer = (thickness of the positive electrode tab - thickness of the positive electrode current collector) / 2.

[0148] In some embodiments, the single-sided coating weight of the positive electrode film layer is 220 mg / 1540.25 mm 2 to 350 mg / 1540.25 mm 2 ; optionally, the single-sided coating weight of the positive electrode film layer is 230 mg / 1540.25 mm 2 to 300 mg / 1540.25 mm 2 . The single-sided coating weight of the positive electrode film layer in the above range is further beneficial to the energy density and fast charging performance of the battery monomer. Exemplarily, the single-sided coating weight of the positive electrode film layer is a value between 220 mg / 1540.25 mm 2 , 230 mg / 1540.25 mm 2 , 250 mg / 1540.25 mm 2 , 270 mg / 1540.25 mm 2 , 290 mg / 1540.25 mm 2 , 300 mg / 1540.25 mm 2 , 320 mg / 1540.25 mm 2 , 340 mg / 1540.25 mm 2 , 350 mg / 1540.25 mm 2 or a range consisting of any two of them.

[0149] In the present application, the "single-sided coating weight of the positive electrode film layer" refers to the weight of the positive electrode film layer per unit area on one side of the positive electrode current collector.

[0150] In the present application, the single-sided coating weight of the positive electrode film layer can be tested by known methods in the art. For example, the positive electrode tab can be obtained from the disassembled battery monomer (if it is a double-sided coated positive electrode tab, the positive active material layer on one side can be wiped off first), punched into small round pieces with an area of S1, weighed, and recorded as M1. Then wipe off the positive electrode film layer of the above weighed positive electrode tab, weigh the mass of the positive electrode current collector, and record it as M0. The single-sided coating weight of the positive electrode film layer = (M1-M0) / S1.

[0151] In some embodiments, the compacted density of the positive electrode tab is 2.4 g / cm 3 to 2.75 g / cm 3 ; optionally, the compacted density of the positive electrode tab is 2.45 g / cm 3 to 2.6 g / cm 3 . In this way, the energy density and fast-charging performance of the battery cell are further balanced. For example, the compacted density of the positive electrode tab is 2.4 g / cm 3 , 2.45 g / cm 3 , 2.5 g / cm 3 , 2.54 g / cm 3 , 2.6 g / cm 3 , 2.65 g / cm 3 , 2.7 g / cm 3 , 2.75 g / cm 3 , or a value between any two of them.

[0152] In the present application, the compacted density of the positive electrode tab is the meaning known in the art, which can be measured by instruments and methods known in the art. The compacted density of the positive electrode tab = the areal density of the positive electrode film layer / the thickness of the positive electrode film layer. The thickness of the positive electrode film layer can be measured by instruments and methods known in the art, for example, a micrometer (e.g., Mitutoyo 293-100, accuracy 0.1 μm) can be used to measure the thickness of the positive electrode tab at at least 12 different positions along the thickness direction of the positive electrode tab, and then the average value is taken as the thickness of the positive electrode tab, and then the thickness of the positive electrode current collector is subtracted to obtain the thickness of the positive electrode film layer. The areal density of the positive electrode film layer can be measured by instruments and methods known in the art, for example, the positive electrode tab after cold pressing or the positive electrode tab obtained after battery disassembly (if it is a double-sided coated positive electrode tab, the positive electrode film layer on one side is wiped off first), is punched into a small disc with an area of S1, and weighed, recorded as M1. Then the positive electrode film layer of the above weighed positive electrode tab is wiped off, and the weight of the positive electrode current collector is weighed, recorded as M0. The areal density of the positive electrode film layer = (M1-M0) / S1.

[0153] In some embodiments, the positive electrode tab further comprises a positive electrode film layer located on at least one side of the positive electrode current collector and comprising a positive electrode active material; the positive electrode active material comprises a lithium-containing olivine phosphate. The lithium-containing olivine phosphate is a positive electrode active material with an olivine structure comprising lithium ions and phosphate groups, which has the advantages of low cost and long service life.

[0154] In some embodiments, the chemical formula of the lithium-containing olivine phosphate is Li x1 A y1 Mea1 M b1 P 1- c1 X c1 Y z1 Wherein, 0.5≤x1≤1.3, 0≤y1≤1.3, 0.9≤x1+y1≤1.3; 0.9≤a1≤1.5, 0≤b1≤0.5, 0.9≤a1+b1≤1.5; 0≤c1≤0.5; 3≤z1≤5; A includes one or more of Na, K and Mg; Me includes one or more of Mn, Fe, Co and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La and Ce; X includes one or more of S, Si, Cl, B, C, N and P; Y includes one or more of O and F.

[0155] In some implementations, x1 can be selected as a value between any two of the following: 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3; y1 can be selected as a value between any two of the following: 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3; x1+y1 can be selected as a value between any two of the following: 0.9, 1, 1.1, 1.2, 1.3; a1 can be selected as a value between any two of the following: 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5; b1 can be... The values ​​can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any two of these values. a1+b1 can be selected as 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or any two of these values. c1 can be selected as 0, 0.1, 0.2, 0.3, 0.4, 0.5, or any two of these values. z1 can be selected as 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, or any two of these values.

[0156] The lithium phosphate with the above-mentioned components and olivine structure has good structural stability, which can reduce losses during fast charging and further improve the fast charging performance and cycle stability of battery cells.

[0157] In the present application, the type of the positive electrode active material can be tested by any method known in the art. As an example, a phase analysis method such as X-ray diffraction (XRD) can be used in combination with an elemental analysis method such as energy spectrum, XPS, etc.

[0158] In some embodiments, the positive electrode active material comprises one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate, and a modified form of any of the foregoing. The modified form includes one or more of a doping modification and a coating modification.

[0159] In some embodiments, the positive electrode active material comprises a modification element, and the modification element comprises one or more of Al, V, Ti, Zr, Hf, Ge, and Sn; optionally, the modification element comprises Al, V, and Ti. In this way, the stability of the positive electrode active material is improved, so that the side reaction between the positive electrode active material and the electrolyte can be reduced, and the cycle performance and energy density of the battery cell can be further improved.

[0160] In some embodiments, the mass percentage of the modification element in the positive electrode active material is 100 ppm to 5000 ppm; optionally, the mass percentage of the modification element in the positive electrode active material is 100 ppm to 3000 ppm. In this way, the cycle performance and energy density of the battery cell can be balanced. For example, the mass percentage of the modification element in the lithium transition metal oxide is 100 ppm, 200 ppm, 500 ppm, 1000 ppm, 1200 ppm, 1500 ppm, 1800 ppm, 2000 ppm, 2500 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, or a value between any two of them.

[0161] In the present application, the type of the modification element and the mass percentage of the modification element in the positive electrode active material can be determined by inductively coupled plasma emission spectrometry (ICP). Specifically, 0.2 g of positive electrode active material powder is weighed into a 100 mL beaker, 10 mL of 10% w / w nitric acid solution is added, and the mixture is heated and digested at 120°C for 0.5 hours. Then, the mixture is diluted to 100 mL with a volumetric flask. 1 mL of the solution is then taken with a pipette and diluted to 100 mL with a volumetric flask to obtain a test solution. Then, the mass fraction of each element in the test solution is determined by inductively coupled plasma emission spectrometry.

[0162] In some embodiments, the positive active material can further include lithium transition metal oxides and modified compounds thereof. Optionally, examples of the lithium transition metal oxides can include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(also can be referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(also can be referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM811), lithium nickel cobalt aluminum oxides (such as LiNi 0.85 Co 0.10 Al 0.05 O2), and modified compounds thereof, and the like.

[0163] In some embodiments, the positive active material includes a lithium-containing olivine phosphate with an olivine structure, and a coating layer located at least partially on a surface of the lithium-containing phosphate, the coating layer including a carbon element. In this way, the electronic conductivity of the lithium transition metal phosphate can be improved by the coating layer, and the solid-phase transmission rate of the electron can be improved, thereby further improving the energy density and fast charging performance of the battery cell.

[0164] In some embodiments, the coating layer further includes a substance with a chemical formula of Li 3-d1 Fe 2-d1 M1 d1 (PO m1 ) n1 , wherein 0≤d1≤1, 3≤m1≤5, 2≤n1≤4, and M1 includes one or more of Ti, Zr, Hf, Ge, Sn, and optionally, M1 is +4 valence.

[0165] In some embodiments, d1 can be selected from 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or a value between any two of them, m1 can be selected from 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, or a value between any two of them, and n1 can be selected from 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, or a value between any two of them.

[0166] In some embodiments, the coating layer can include one or more of Li2FeTi(PO4)3, Li2FeZr(PO4)3, Li2FeSn(PO4)3.

[0167] It should be noted that the coating layer can be a single-layer structure or a multi-layer structure, that is, the carbon-containing component in the coating layer and the component shown in Formula I can be in a mixed phase or can be arranged in layers.

[0168] The phase structure in the coating layer can be characterized by any known method in the art, for example, by characterizing the positive electrode active material by transmission electron microscopy, it can be seen that the coating layer and the matrix of the positive electrode active material have different phase structures, and the components of the coating layer can be determined by combining diffraction patterns and energy spectrum analysis.

[0169] In this application, the battery will be accompanied by Li deintercalation and consumption during charging and discharging, and the molar content of Li is different when the battery is discharged to different states. In the enumeration of the positive electrode active material in this application, the molar content of Li is the initial state of the material, that is, the state before feeding, and the positive electrode active material is applied to the battery system, and after charging and discharging cycle, the molar content of Li will change.

[0170] In the enumeration of the positive electrode active material in this application, the molar content of O is only the theoretical state value, and the lattice oxygen release will cause the change of the molar content of oxygen, and the actual molar content of O will appear floating.

[0171] In some embodiments, the positive electrode current collector has two opposite surfaces in the thickness direction of itself, and the positive electrode active material is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.

[0172] As an example, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as a metal foil, silver surface-treated aluminum or stainless steel, stainless steel, copper, nickel, or titanium, etc. can be employed. The composite current collector can include a high molecular material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a high molecular material base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0173] In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0174] In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0175] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode tab can be obtained.

[0176] In some embodiments, the positive electrode tab further includes a positive electrode conductive layer, and the positive electrode conductive layer is located between the positive electrode current collector and the positive electrode film layer. The arrangement of the positive electrode conductive layer is conducive to improving the electronic conductivity of the battery monomer tab, and is conducive to further improving the fast charging performance of the battery monomer.

[0177] In some embodiments, the negative electrode tab further includes a negative electrode conductive layer, and the negative electrode conductive layer is located between the negative electrode current collector and the negative electrode film layer. The arrangement of the negative electrode conductive layer is conducive to improving the electronic conductivity of the battery monomer tab, and is conducive to further improving the fast charging performance of the battery monomer.

[0178] In some embodiments, the positive electrode tab includes a positive electrode conductive layer, and the negative electrode tab includes a negative electrode conductive layer. In this way, the fast charging performance of the battery monomer is more conducive to being improved.

[0179] In some embodiments, the thickness of the positive electrode conductive layer is 0.1-5 μm, and optionally, the thickness of the positive electrode conductive layer is 0.2-4 μm. In this way, the fast-charging performance of the battery cell is more improved. Exemplarily, the thickness of the positive electrode conductive layer is 0.2 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.5 μm, 5.8 μm, 5.0 μm, or a value between any two of them.

[0180] In some embodiments, the thickness of the negative electrode conductive layer is 0.1-5 μm, and optionally, the thickness of the negative electrode conductive layer is 0.2-4 μm. In this way, the fast-charging performance of the battery cell is more improved. Exemplarily, the thickness of the negative electrode conductive layer is 0.2 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.5 μm, 5.8 μm, 5.0 μm, or a value between any two of them.

[0181] In some embodiments, the positive electrode conductive layer comprises a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent comprises one or more of super conductive carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and the positive electrode binder comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a polyacrylic acid, and a fluorine-containing acrylic ester resin.

[0182] In some embodiments, the negative electrode conductive layer comprises a negative electrode conductive agent and a negative electrode binder. The negative electrode conductive agent comprises one or more of super conductive carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and the negative electrode binder comprises at least one of a styrene butadiene rubber, a polyacrylic acid, a sodium polyacrylate, a polyacrylamide, a polyvinyl alcohol, a sodium alginate, a polymethacrylic acid, and a carboxymethyl chitosan.

[0183] In some embodiments, the battery cell further comprises an electrolyte, the electrolyte comprising a lithium-containing electrolyte salt; the lithium-containing electrolyte salt comprising one or more of a fluorine-containing sulfimide salt, lithium hexafluorophosphate. The fluorine-containing sulfimide salt in the above lithium-containing electrolyte salt contains a strong electron-withdrawing group, which can improve its own dissociation ability in the solvent, thereby improving the conductivity of the electrolyte. At the same time, the fluorine-containing sulfimide salt can generate a solid electrolyte interface film (SEI film) rich in lithium fluoride and lithium oxide at the negative electrode film layer, which can not only improve the lithium ion intercalation rate under fast charging, but also improve the stability of the SEI, which is conducive to the improvement of the fast charging performance and cycle performance of the battery cell. In addition, the use of fluorine-containing sulfimide salt and lithium hexafluorophosphate together can further improve the conductivity of the electrolyte, and further enhance the stability of the anode SEI film, thereby more conducive to improving the cycle performance and fast charging performance of the battery cell.

[0184] In some embodiments, the mass fraction of the lithium-containing electrolyte salt is 10% to 20% based on the total mass of the electrolyte. Alternatively, the mass fraction of the lithium-containing electrolyte salt is 13% to 17.5% based on the total mass of the electrolyte. The mass fraction of the lithium-containing electrolyte salt in the above range can further balance the fast charging performance and cycle stability of the battery cell. For example, the mass fraction of the lithium-containing electrolyte salt is 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 17.5%, 18%, 19%, 20% or a value between any two of them.

[0185] In some embodiments, the lithium-containing electrolyte salt comprises a fluorine-containing sulfimide salt and lithium hexafluorophosphate; the mass ratio of the fluorine-containing sulfimide salt and lithium hexafluorophosphate is (1:4) to (4:1) based on the total mass of the lithium-containing electrolyte salt, and optionally, the mass ratio of the fluorine-containing sulfimide salt and lithium hexafluorophosphate is (1:3) to (3:4). Thus, it is conducive to further improving the fast charging performance and cycle performance of the battery cell. For example, the mass ratio of the fluorine-containing sulfimide salt and lithium hexafluorophosphate is 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5, 1:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 or a value between any two of them based on the total mass of the lithium-containing electrolyte salt.

[0186] In some embodiments, the electrolyte includes a solvent, and the solvent includes a carboxylic acid ester solvent and / or a carbonate solvent. The carboxylic acid ester solvent has the advantages of low viscosity and high ionic conductivity, which is conducive to the infiltration of the electrolyte into the negative active material layer and the fast charging and embedding and disembedding of active ions in the negative active material layer, thereby further improving the lithium precipitation problem of the negative electrode sheet. The carbonate solvent has a high dielectric constant, which can increase the dissociation speed of lithium ions and anions in the lithium-containing electrolyte salt, thereby further comprehensively improving the fast charging performance of the battery cell and the cycle stability under fast charging.

[0187] In some embodiments, the carboxylic acid ester solvent has a general structural formula of R'-COO-R'', wherein R' includes one or more of a hydrogen atom, a halogen atom, a C1-C5 alkyl group, and a C1-C5 halogenated alkyl group, and R'' includes one or more of a C1-C5 alkyl group and a C1-C5 halogenated alkyl group.

[0188] Herein, “C1-C5 alkyl group” refers to an unbranched or branched alkyl group having 1-5 carbon atoms, including but not limited to one or more of a methyl group, an ethyl group, a propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl group, a n-pentyl group, a 2-pentyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1,2-dimethylpropyl group, a 1,1-dimethylpropyl group, a 2,2-dimethylpropyl group, and a 1-ethylpropyl group.

[0189] Herein, “C1-C5 halogenated alkyl group” refers to an unbranched or branched alkyl group having 1-5 carbon atoms, in which at least one hydrogen atom is replaced by a halogen, including but not limited to one or more of a chloroalkyl group, a bromoalkyl group, and an iodoalkyl group. “Halogen” refers to an element in Group VIIA of the periodic table of chemical elements, specifically, the halogen includes fluorine, chlorine, bromine, iodine, and the like.

[0190] In some embodiments, the carboxylic acid ester solvent includes one or more of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

[0191] In some embodiments, the carbonate solvent includes one or more of vinyl carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0192] In some embodiments, the mass percentage of the solvent is 72%-89.95% based on the total mass of the electrolyte, and optionally, the mass percentage of the solvent is 78%-88% based on the total mass of the electrolyte. In this way, the electrolyte has good conductivity and stability, which is conducive to further improving the fast-charging performance and cycle performance of the battery cell. For example, the mass percentage of the solvent is 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 89.5% or a value between any two of the above values based on the total mass of the electrolyte.

[0193] In some embodiments, the lithium-containing electrolyte salt comprises a carboxylic ester solvent and a carbonate solvent, and the mass ratio of the carboxylic ester solvent to the carbonate solvent is (1:6) to (1:1) based on the total mass of the solvent, and optionally, the mass ratio of the carboxylic ester solvent to the carbonate solvent is (1:5) to (1:3) based on the total mass of the solvent. In this way, the electrolyte has good conductivity, stability and appropriate viscosity, which is conducive to further improving the fast-charging performance and cycle performance of the battery cell. For example, the mass ratio of the carboxylic ester solvent to the carbonate solvent is 1:6, 1:5.5, 1:5, 1:4.5, 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5, 1:1 or a value between any two of the above values based on the total mass of the solvent.

[0194] In the present application, the types and contents of inorganic components / lithium salt in the electrolyte are the meanings known in the art, which can be detected by using the devices and methods known in the art, for example, the qualitative or quantitative analysis of the inorganic components / lithium salt in the electrolyte can be performed by ion chromatography according to the standard JY / T020-1996 "General Ion Chromatography Analysis Method". In the embodiments of the present application, the freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or the free electrolyte obtained from a battery that has been discharged (discharged to the lower limit cutoff voltage so that the charged state of the battery is about 0% SOC) can be taken as a sample, and the ion chromatography method is used for detection. In the embodiments of the present application, the types and contents of organic components in the electrolyte are the meanings known in the art, which can be detected by using the devices and methods known in the art, for example, the qualitative and quantitative analysis of the organic components in the electrolyte can be performed by gas chromatography according to the standard GB / T9722-2006 "General Gas Chromatography Method for Chemical Reagents".

[0195] In the embodiments of the present application, after the components in the electrolyte are quantitatively and qualitatively detected, the components are classified, and the chain carboxylate solvents and the carbonate solvents are taken as the constituent components of the organic solvents. The mass content of each component is calculated based on 100% of the mass of the organic solvents.

[0196] It should be noted that the mass ratio of the above-mentioned lithium-containing electrolyte salt in the electrolyte, the mass ratio of the fluorine-containing sulfimide salt and lithium hexafluorophosphate, the mass ratio of the solvent, and the mass ratio of the carboxylate solvents and the carbonate solvents are all the added amounts. In the actual reverse test, the mass ratio of the lithium-containing electrolyte salt in the electrolyte, the mass ratio of the fluorine-containing sulfimide salt and lithium hexafluorophosphate, the mass ratio of the solvent, and the mass ratio of the carboxylate solvents and the carbonate solvents that can be detected and calculated may be less than or more than the actual added amount. However, the content of each component obtained by the reverse test should not differ too much from the actual added amount, and the error should be within a reasonable range.

[0197] In some embodiments, the electrolyte includes an additive, and the additive includes one or more of a lithium salt additive, a carbonate additive, and a sulfur-containing additive.

[0198] In some embodiments, the lithium salt additive includes one or more of lithium difluorophosphate, lithium difluoro oxalate borate, lithium tetrafluoroborate, and lithium bis-oxalate borate. The lithium salt additive can evolve into inorganic components in the SEI film, improve the rigidity and thermal stability of the SEI film, further improve the stability of the SEI film, further reduce the interface impedance on the negative electrode side, and thus further improve the cycle stability and fast charging performance of the battery cell. In addition, the above-mentioned lithium salt additive can also form a positive electrolyte interface film (CEI film) on the surface of the positive active material, thereby further improving the cycle stability of the battery cell.

[0199] In the present application, the carbonate additive refers to a compound including a carbonate group (-O-CO-O-) and derivatives thereof, as well as mixtures containing the above-mentioned compound and derivatives thereof. In some embodiments, the carbonate additive includes one or more of vinylene carbonate (VC) and a vinyl carbonate derivative. The carbonate additive can evolve into organic components in the SEI film, improve the toughness of the SEI film, and thus further improve the stability of the SEI film during the cycle process of the battery cell, further reduce the interface impedance on the negative electrode side, and be conducive to further improving the cycle life and fast charging performance of the battery cell.

[0200] In some embodiments, the sulfur-containing additive includes one or more of vinyl sulfates, bis vinyl sulfates, butylene sulfite, ethylene sulfite, methylidene methanesulfonate, 1,3 propanesultone. The sulfur-containing additive has a higher potential, and the sulfur-containing additive added in the electrolyte will preferentially react during formation or subsequent cycling, evolving into a sulfur-containing component in the SEI film. The SEI film containing sulfur can further improve the thermal stability of the SEI film at high temperatures, further reduce the interfacial impedance on the negative side, and is beneficial to further improve the cycle stability and fast charging performance of the battery cell.

[0201] In some embodiments, the mass fraction of the additive is 0.1%-7% based on the total mass of the electrolyte; optionally, the mass fraction of the additive is 1%-5% based on the total mass of the electrolyte. Thus, it is beneficial to further balance the cycle stability and fast charging performance of the battery cell. Exemplarily, the mass fraction of the additive is 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0% or a value between any two of them.

[0202] In some embodiments, the electrolyte includes a lithium salt additive; the mass fraction of the lithium salt additive is 0.1%-3% based on the total mass of the electrolyte; optionally, the mass fraction of the lithium salt additive is 0.8%-2.5% based on the total mass of the electrolyte. Thus, it is further beneficial to improve the cycle stability and fast charging performance of the battery cell. Exemplarily, the mass fraction of the lithium salt additive is 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.5%, 3.0% or a value between any two of them based on the total mass of the electrolyte.

[0203] In some embodiments, the lithium salt additive includes one or more of lithium difluorophosphate, lithium difluoro oxalate borate, lithium tetrafluoroborate, lithium bisoxalate borate.

[0204] In some embodiments, the lithium salt additive comprises lithium difluoro(oxalato)borate; the mass fraction of lithium difluoro(oxalato)borate in the electrolyte is 0.1%-1.5% based on the total mass of the electrolyte; optionally, the mass fraction of lithium difluoro(oxalato)borate in the electrolyte is 0.5%-1.2% based on the total mass of the electrolyte. The mass fraction of lithium difluoro(oxalato)borate in the electrolyte within the above range is conducive to improving the stability of the SEI film and the viscosity of the electrolyte, and further conducive to comprehensively improving the cycle life and fast charging performance of the battery cell. Illustratively, the mass fraction of lithium difluoro(oxalato)borate in the electrolyte is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a value between any two of them.

[0205] The components of the additive can be tested in any known manner in the art. In embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, the free electrolyte of a fresh battery can be taken as a sample, or the free electrolyte obtained from a battery cell that has been discharged (discharged to the discharge cut-off voltage so that the charged state of the battery cell is about 0% SOC) can be taken as a sample, and ion chromatography analysis method can be used for detection. The types and contents of organic components in the electrolyte are known in the art, and can be detected using known devices and methods in the art, for example, qualitative and quantitative analysis of organic components in the electrolyte can be performed by gas chromatography according to GB / T 9722-2023 "General rules for gas chromatography of chemical reagents". The types and contents of inorganic components / lithium salts in the electrolyte are known in the art, and can be detected using known devices and methods in the art, for example, qualitative or quantitative analysis of inorganic components / lithium salts in the electrolyte can be performed by ion chromatography according to standard JY / T 020-2002 "General rules for ion chromatography analysis method".

[0206] It should be noted that the additive content mentioned in the technical solution of the present application is the content of the additive actively added to the fresh electrolyte. However, due to the consumption of the additive in the electrolyte during formation and charge-discharge cycling, relevant components are generated in the SEI film and / or CEI film, and when the content of the sulfur-containing additive is tested by gas chromatography after the electrolyte is obtained by disassembling the battery cell, the content may

[0207] Specifically, taking the case of 0% of the mass content of the sulfur-containing additive as an example, it can be that no sulfur-containing additive is added in the freshly prepared electrolyte, or it can be that no sulfur-containing additive is contained in the electrolyte obtained after disassembling the battery cell. This case can be that the freshly prepared electrolyte does not add the sulfur-containing additive, or a small amount of sulfur-containing additive is added, but participates in the SEI film forming reaction in the battery cell formation process, so that the mass content of the sulfur-containing additive is 0% in the detection process.

[0208] Further, for adding certain substances, such as additives, in the electrolyte, due to the characteristics that the additives participate in the film forming on the surface of the active material, the content of the additives in the battery cell electrolyte is related to the formation, different battery life cycles or different battery storage states, so the content of the additives in the freshly prepared electrolyte can be different from the content of the additives in the electrolyte obtained by disassembling the battery cell in reverse, but the person skilled in the art can know the approximate range of the content of the related substances in the freshly prepared electrolyte according to the performance level of the battery cell (such as the number of cycles), the residual content, etc. Similarly, the person skilled in the art can also know the approximate range of the content of the non-freshly prepared (i.e. after reverse) according to the content of the freshly prepared additive, according to the performance requirements of the battery cell, the storage environment, etc.

[0209] It can be understood that in some embodiments, the sulfur-containing additive added in the electrolyte is completely converted into the SEI film in the formation process, and it can be inferred that the sulfur-containing additive is added in the electrolyte by X-ray photoelectron spectroscopy (XPS) test of the negative electrode material. In some embodiments, the sulfur-containing additive remains in the electrolyte, and forms a reinforcing effect on the SEI film in the subsequent battery cell cycle process.

[0210] In this application, the X-ray photoelectron spectroscopy (XPS) of the negative electrode material can be tested by any known method in the art. As an example, after the battery cell is disassembled, the negative electrode sheet is cleaned with a solvent such as dimethyl carbonate (DMC) for more than three times, and then the powder is scraped and sampled. The obtained negative electrode material sample powder is adhered to a conductive substrate, and X-ray photoelectron spectroscopy (such as AXIS ULTRA) is used for X-ray photoelectron spectroscopy test. The scanning rate and time of the X-ray source are adjusted so that it focuses and detects the elements and functional groups in the depth of 5nm-10nm from the surface of the negative electrode material, obtains the X-ray photoelectron spectroscopy (XPS) spectrum of the sample, and analyzes the element characteristic peaks in the spectrum.

[0211] In some embodiments, the electrolyte has an electrical conductivity of 10-20 mS / cm, and optionally, the electrolyte has an electrical conductivity of 12-17 mS / cm. In this way, the fast-charging performance and cycle performance of the battery cell are further improved. For example, the electrolyte has an electrical conductivity of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 mS / cm or a value between any two of the above values.

[0212] In this application, the electrical conductivity of the electrolyte can be tested according to HG / T 4067-2015 using a conductivity meter. Specifically, the battery is disassembled, and the electrolyte to be tested is obtained. About 100 mL of the electrolyte to be tested is taken in a dry and clean corrosion-resistant sample bottle and placed in a constant-temperature water bath at 25±0.5°C. When the temperature of the electrolyte to be tested is constant, the sample bottle cap is replaced with a rubber plug with an electrode. When the temperature is within 25±0.5°C, the data is read, and the electrical conductivity of the electrolyte to be tested is obtained.

[0213] In some embodiments, the electrode assembly further comprises a separator film, the separator film comprising a base film and a coating layer disposed on at least one side of the base film; the coating layer comprising a ceramic coating layer and an aqueous adhesive layer, the ceramic coating layer being disposed between the base film and the aqueous adhesive layer. In some embodiments, the ceramic coating layer comprises a ceramic material, the ceramic material comprising one or more of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide. In some embodiments, the aqueous adhesive layer comprises an adhesive material, the adhesive material comprising one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer. The ceramic coating layer has good wettability, which can promote the absorption of the electrolyte during the cycle process and improve the liquid retention capacity of the separator film, thereby reducing the risk of lithium precipitation during the cycle process and improving the fast-charging performance and cycle performance of the battery cell. The aqueous adhesive layer has good film-forming property and interfacial adhesion, which can "anchor" the ceramic particles on the surface of the base film through intermolecular forces and bond the ceramic particles to each other to form a continuous and firm ceramic coating layer. In this way, the fast-charging performance and cycle performance of the battery cell are further improved.

[0214] Figure 4 is a schematic diagram of the cross-sectional structure of the separator film according to an embodiment of the present application, referring to Figure 4 The separator film 30 comprises a base film 301 and a coating layer 302 disposed on both sides of the base film 301; the coating layer 302 comprises a ceramic coating layer 3021 and an aqueous adhesive layer 3022, and the ceramic coating layer 3021 is disposed between the base film 301 and the aqueous adhesive layer 3022.

[0215] It should be noted that, Figure 4 The diagram illustrates the structure of the isolation membrane 30, the ceramic coating 3021, and the water-based adhesive layer 3022. In reality, there is no clear boundary between the ceramic coating 3021 and the water-based adhesive layer 3022, and the ceramic coating 3021 and the water-based adhesive layer 3022 overlap in their thickness direction.

[0216] In this application, the presence of the ceramic coating and the water-based adhesive layer can be determined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) of the cross-section of the isolation membrane.

[0217] In some embodiments, the thickness of the base film is 5 μm to 10 μm; optionally, the thickness of the base film is 5.5 μm to 8.5 μm. This is beneficial for further balancing the energy density, fast charging performance, and cycle stability of the battery cell. Exemplarily, the thickness of the base film is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a value within a range of any two of these values.

[0218] In some embodiments, the thickness of the single-sided coating is from 0.5 μm to 3 μm; optionally, the thickness of the base film is from 1.5 μm to 2.5 μm. This is beneficial for further balancing the safety performance and energy density of the battery cell. Exemplarily, the coating thickness is 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3.0 μm, or a value within a range of any two of these values.

[0219] In some embodiments, the porosity of the separator is 20% to 60%; alternatively, the porosity is 25% to 45%. This is beneficial for further balancing the energy density, fast-charging performance, and cycle stability of the battery cells. Exemplarily, the porosity of the separator is a value between 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, or any two of these values.

[0220] In this application, porosity refers to the percentage of the volume of the pores in the separator to the total volume of the separator. Porosity can be tested according to the standard GB / T 36363-2018 "Polyolefin Separators for Battery Cells". It should be noted that the actual testing process may differ slightly from the standard due to differences in testing instruments, testing errors, and to minimize the impact on porosity testing, in order to obtain more accurate test values.

[0221] In some embodiments, the battery cell comprises a shell and a cover plate assembly, the cover plate assembly is arranged at least one end of the shell, the shell and the cover plate assembly define a receiving cavity, an electrode assembly is arranged in the receiving cavity, the shell wall thickness of the battery cell large face is 0.4mm to 0.65mm; optionally, the shell wall thickness of the battery cell large face is 0.45mm to 0.6mm. Thus, it is conducive to further improvement of the energy density of the battery cell. Exemplarily, the shell wall thickness of the battery cell large face is 0.4mm, 0.45mm, 0.5mm, 0.55mm, 0.60mm, 0.65mm or a value between any two of them.

[0222] In some embodiments, the cover plate assembly comprises a cover plate, a first electrode terminal and a second electrode terminal, the polarity of the first electrode terminal is opposite to that of the second electrode terminal. Thus, the temperature rise of the battery cell and the impedance of the battery cell can be reduced during charging, which is conducive to the improvement of the fast charging performance, cycle life and safety performance of the battery cell.

[0223] In some embodiments, the first electrode terminal can be a positive electrode terminal connected to the positive electrode tab through an adapter sheet, and the second electrode terminal can be a negative electrode terminal connected to the negative electrode tab through an adapter sheet.

[0224] In some embodiments, the minimum cross-sectional area S of the first electrode terminal and / or the second electrode terminal satisfies: 600mm 2 ≤S≤1100mm 2 ; optionally, the minimum cross-sectional area S of the first electrode terminal and / or the second electrode terminal satisfies: 750mm 2 ≤S≤950mm 2 . Thus, it is conducive to improve the overcurrent capacity of the battery cell, reduce the heat generation of the electrode terminal, reduce the internal resistance of the battery cell, and thus improve the fast charging performance and cycle stability of the battery cell. Exemplarily, the minimum cross-sectional area S of the first electrode terminal and / or the second electrode terminal is 600mm 2 , 650mm 2 , 700mm 2 , 750mm 2 , 800mm 2 , 850mm 2 , 900mm 2 , 950mm 2 , 1000mm 2 , 1050mm 2 , 1100mm 2 or a value between any two of them.

[0225] In the present application, the minimum cross-sectional area of the first electrode terminal refers to the minimum cross-sectional area of the first electrode terminal in the direction perpendicular to the current flow direction, and the minimum cross-sectional area of the second electrode terminal refers to the minimum cross-sectional area of the second electrode terminal in the direction perpendicular to the current flow direction.

[0226] In the present application, when testing the minimum cross-sectional area of the first electrode terminal and / or the second electrode terminal, the minimum cross-sectional area can be calculated according to the shape of the minimum cross-sectional area and the area calculation formula thereof. For example, if the minimum cross-sectional area of the electrode terminal is circular, the minimum cross-sectional area can be obtained by measuring the radius of the circle, and if the minimum cross-sectional area is square, the minimum cross-sectional area can be obtained by measuring the length and width of the square.

[0227] In some embodiments, the volume ratio of the electrode assembly in the accommodation cavity is 75%-90%; optionally, the volume ratio of the electrode assembly in the accommodation cavity is 80%-88%. The volume ratio of the electrode assembly in the accommodation cavity reflects the space utilization rate of the accommodation cavity. When the space utilization rate of the accommodation cavity is within the above range, on the one hand, it is beneficial to the volume energy density of the battery monomer, and on the other hand, it makes there is enough space for liquid injection in the accommodation cavity, which is beneficial to the improvement of the fast charging performance, cycle performance and safety performance of the battery monomer. Exemplarily, the volume ratio of the electrode assembly in the accommodation cavity is 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90% or a value between any two of them.

[0228] It should be noted that the volume of the electrode assembly = the length of the winding core * the width of the winding core * the height of the winding core * the number of winding cores. The volume of the accommodation cavity = the length of the accommodation cavity * the width of the accommodation cavity * the height of the accommodation cavity. The accommodation cavity is defined by the shell of the battery monomer and the cover plate assembly. It should also be noted that the winding core in the above formula does not specifically refer to the core structure formed by winding, but also includes the core structure formed by laminating, which is collectively referred to as "winding core" for convenience of description.

[0229] In some embodiments, the battery monomer can include an outer package. The outer package can be used to package the above-mentioned electrode assembly and electrolyte.

[0230] In some embodiments, the outer package of the battery monomer can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery monomer can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0231] The shape of the battery monomer is not particularly limited in the present application, which can be cylindrical, square or any other shape. For example, Figure 5 is a schematic diagram of a battery monomer according to an embodiment of the present application,Figure 5 A battery cell 5 of a square structure is exemplarily shown.

[0232] Figure 6 is Figure 5 A battery cell of an embodiment of the present application is shown in an exploded view. Referring to Figure 6 The outer package can include a housing 51 and a top cover assembly 53. The housing 51 can include a bottom plate and side plates connected to the bottom plate, which enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be arranged on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can form an electrode assembly 52 through a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by a person skilled in the art according to specific actual needs.

[0233] Battery apparatus

[0234] A second aspect of an embodiment of the present application provides a battery apparatus. The battery apparatus in the embodiment of the present application can include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly can include a plurality of battery cells provided by the first aspect, and the plurality of battery cells are connected in series, in parallel, or in a mixed connection through a busbar component.

[0235] In some embodiments, the battery cell assembly is generally formed by arranging a plurality of battery cells.

[0236] As an example, the battery cell assembly can be a battery module, which is formed by arranging and fixing a plurality of battery cells into an independent module. As an example, the battery module can be formed by bundling a plurality of battery cells with a cable tie.

[0237] As an example, the battery cell assembly can be a battery module, which can be accommodated in a box by fixing the battery module in the box.

[0238] As an example, the battery cell assembly can also be accommodated in a box by directly fixing a plurality of battery cells in the box.

[0239] As an example, the box can include a first box and a second box. The first box and the second box are buckled so that a closed space is formed inside the box to accommodate the battery cell assembly. Here, closed means covered or closed, which can be sealed or unsealed. The first box can be a top cover or a bottom plate.

[0240] As an example, the box can include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are connected with the frame, respectively, so that an enclosed space is formed inside the box to accommodate the battery cell assembly.

[0241] In some embodiments, the box can be part of a chassis structure of a vehicle. For example, part of the box can be at least part of a floor of the vehicle, or part of the box can be at least part of a cross beam and a longitudinal beam of the vehicle.

[0242] In some embodiments, the battery device can be a battery pack including the box and one or more battery cell assemblies accommodated in the box.

[0243] The technical solutions described in the embodiments of the present application are applicable to various battery cell using electric devices, such as mobile phones, portable devices, notebook computers, electric vehicles, electric toys, electric tools, vehicles, ships, and spacecraft, such as aircraft, rockets, space shuttles, and spaceships.

[0244] Figure 7 is a schematic diagram of a battery module according to an embodiment of the present application, referring to Figure 7 In the battery module 4, the plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0245] Optionally, the battery module 4 can further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0246] Figure 8 is a schematic diagram of a battery pack according to an embodiment of the present application, Figure 9 is Figure 8 is an exploded view of the battery pack according to an embodiment of the present application, referring to Figure 8 and Figure 9 In the battery pack 1, a battery box and a plurality of battery modules 4 arranged in the battery box can be included. The battery box includes a first box 2 and a second box 3, and the first box 2 can be arranged on the second box 3 to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0247] Electric device

[0248] The third aspect of the embodiments of the present application further provides an electric device, which will be described below with reference to the accompanying drawings.

[0249] The power-using device mentioned in the embodiments of the present application includes the battery device provided in the second aspect of the present application. The battery device can be used as a power source of the power-using device, or can be used as an energy storage unit of the power-using device. The power-using device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0250] Figure 10 FIG. 1 is a schematic diagram of a power-using device using the battery cell as a power source according to an embodiment of the present application. The power-using device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of high power and high energy density of the power-using device, a battery pack or a battery module can be used.

[0251] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a battery cell can be used as a power source.

[0252] The battery device of the above-mentioned second aspect can be used as an energy storage device for storing electric energy. As an example, the energy storage device can be, but is not limited to, an energy storage container, an energy storage cabinet, an energy storage power station, an energy storage battery pack, or a portable energy storage system, etc.

[0253] Embodiments

[0254] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If a specific technology or condition is not mentioned in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not mentioned by the manufacturer, it is a conventional product that can be obtained by purchase.

[0255] Embodiment 1

[0256] (1) Preparation of the negative electrode sheet

[0257] The negative active material graphite material, the binder styrene-butadiene rubber, the thickening agent sodium carboxymethyl cellulose (CMC-Na), and the conductive agent superconducting carbon are uniformly mixed according to 97.5:0.5:1:1 and dissolved in deionized water, mixed in a vacuum stirrer, and a uniform negative electrode slurry is formed. The negative electrode slurry is coated on the surface of a negative electrode current collector copper foil with a thickness of 4.5 μm, dried to form a negative electrode film layer. Then, through processes such as rolling and cutting, a negative electrode tab is formed. The negative electrode tab after cutting includes a plurality of negative electrode tabs, and the width (i.e., the size wl of the negative electrode tab along the second direction) of each negative electrode tab is 42 mm. The size L1 of the negative electrode film layer along the first direction is 94 mm. The single-sided coating weight of the negative electrode film layer is 133 mg / 1540.25 mm 2 , and the compaction density of the negative electrode tab is 1.43 g / cm 3 . The volume particle size distribution Dv50 of the graphite material is 10.2 μm, and the specific surface area of the graphite material is 1.1 cm 2 / g.

[0258] (2) Preparation of a positive electrode tab

[0259] The positive active material, conductive carbon, and binder PVDF are mixed in a mass ratio of 98:1:1, a solvent N-methyl pyrrolidone (NMP) is added, and the system is stirred under the action of a vacuum stirrer until it is uniform to obtain a uniform positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of an aluminum foil with a thickness of 13 μm, dried at room temperature, transferred to an oven for further drying, and then subjected to processes such as rolling and cutting to form a positive electrode tab. The positive active material includes LiFeTiPO4 with a carbon coating layer, wherein Ti is a doping element and the content of Ti is 0.2%, and the mass ratio of the carbon coating layer is 1.3%. The positive electrode tab after cutting includes one positive electrode tab, and the width (i.e., the size w3 of the positive electrode tab along the second direction) of the positive electrode tab is 42 mm. The size L2 of the positive electrode film layer along the first direction is 89 mm. The single-sided coating weight of the positive electrode film layer is 290 mg / 1540.25 mm 2 ; and the compaction density of the positive electrode tab is 2.54 g / cm 3 .

[0260] (3) Preparation of a separator film

[0261] A 7 μm polyethylene film is used as a base film, and 2 μm coating layers are provided on both sides of the base film. The coating layers include a ceramic coating layer and a water-based adhesive layer, and the ceramic coating layer is provided between the base film and the water-based adhesive layer. The total thickness of the separator film is 11 μm.

[0262] (4) Preparation of an electrolyte

[0263] Ethyl acetate, dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate are mixed in a mass ratio of 20:35:35:10 to form an organic solvent, and then 5% lithium difluorosulfonimide LiFSi and 10% LiPF6 and 0.2% of the additive lithium difluorophosphate borate are dissolved in the organic solvent to form an electrolyte. The conductivity of the electrolyte is 15 mS / cm.

[0264] (5) Preparation of battery monomer

[0265] The above positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and a winding process is performed to obtain a roll core. Two roll cores are placed in mirror symmetry, and the positive electrode tabs and the negative electrode tabs are ultrasonically welded to the adapter tabs and then folded and fixed with adhesive. Then, an insulating film is wrapped on the outside to form a double-roll electrode assembly. Next, the double-roll electrode assembly is placed in an outer shell, and after drying, an electrolyte is injected. After vacuum packaging, standing, formation, and shaping processes, a battery monomer is obtained. The electrode assembly has a size w2 of 200 mm in the second direction, w1 / w2 is 21%, and w3 / w2 is 21%. In the electrode assembly, each negative electrode tab in each circle has one negative electrode tab, and each positive electrode tab in each circle has one positive electrode tab. The battery monomer uses an aluminum shell, and the shell wall thickness of the large surface of the battery monomer is 0.532 mm. The cover assembly includes a cover, a first electrode terminal, and a second electrode terminal, and the polarity of the first electrode terminal and the second electrode terminal is opposite. The minimum cross-sectional area of the first electrode terminal and / or the second electrode terminal is S, which is 850 mm 2 . The shell and the cover assembly define a containing cavity, and the volume of the containing cavity is 1092 cm 3 . The volume of the electrode assembly is 920 cm 3 , and the volume ratio of the electrode assembly in the containing cavity is 84.2%.

[0266] Pole piece performance parameter test

[0267] The above battery monomer is discharged to 0% SOC, and then the double-sided coated positive electrode sheet and the double-sided coated negative electrode sheet are obtained by disassembling the battery monomer for the following tests:

[0268] (1) Single-sided film layer thickness test

[0269] The thickness of at least 12 different positions along the thickness direction of the negative electrode sheet / positive electrode sheet is measured using a micrometer, and then the average value is taken as the thickness of the negative electrode sheet / positive electrode sheet. The thickness of the single-sided negative electrode film layer is = (thickness of the negative electrode sheet-thickness of the negative current collector) / 2, and the thickness of the single-sided positive electrode film layer is = (thickness of the positive electrode sheet-thickness of the positive current collector) / 2.

[0270] After testing and calculation, the thickness of the single-sided negative electrode film layer in Example 1 is 63 μm, and the thickness of the single-sided positive electrode film layer in Example 1 is 77 μm.

[0271] (2) OI value test of the negative electrode tab

[0272] The XRD test of the negative electrode tab is performed by an X-ray powder diffractometer to obtain an X-ray diffraction spectrum, and then the OI value is calculated according to OI = I 004 / I 110 The ratio of the intensity of the 004 crystal face diffraction peak to the intensity of the 110 crystal face diffraction peak of the negative electrode active material layer is obtained, wherein I 004 is the intensity of the 004 crystal face diffraction peak, and I 110 is the intensity of the 110 crystal face diffraction peak.

[0273] After testing, the OI value of the negative electrode tab in Example 1 is 11.65.

[0274] (3) Porosity test of the negative electrode tab

[0275] The negative electrode tab is cleaned by immersing in ethyl methyl carbonate (EMC); the test instrument is a true density instrument (American Mac AccuPyc II 1340) based on the gas displacement method. The percentage of the pore volume in the negative electrode tab to the total volume of the negative electrode tab is the porosity of the negative electrode tab, and the calculation formula is: porosity = (V-V0) / V x 100%, wherein V0 is the true volume of the negative electrode tab, and V is the apparent volume of the negative electrode tab.

[0276] After testing, the porosity of the negative electrode tab in Example 1 is 28.9%.

[0277] Battery cell performance test

[0278] (1) Capacity test

[0279] After aging, the battery cell is placed at 25°C for 2h, then the battery cell is charged to 3.65V at 0.33C, then constant voltage charged to 0.05C, and then discharged to 2.0V at 0.33C, and the average of the discharge capacity of 3 times is taken as the cell capacity C.

[0280] (2) Direct current resistance (DCR) test

[0281] At 25°C, the battery cell is charged to 3.65V at 0.33C constant current, and then rested for 1 min; then charged to 3.65V at 0.1C constant current, and then rested for 30 min; discharged to 2.0V at 0.33C constant current, and then recorded the discharge capacity A0, unit Ah, and then charged 0.5A0Ah at 0.33C constant current, and adjusted the SOC to 50%.

[0282] The 50% SOC battery cell is placed at 25°C for 2h, then a pulse of 4C current is applied for 10s, and the voltage drop AVdischarge of the battery cell during discharging is recorded; DCR = voltage drop during discharging / discharge current I. The smaller the DC resistance, the better the fast-charging performance of the battery cell under the corresponding current. The test results are shown in Table 2 below.

[0283] (3) Lithium precipitation condition test

[0284] The battery cell is charged at an ambient temperature of 30°C, and the charging steps include the following steps:

[0285] Charged from 0% SOC to 10% SOC at a constant current of 5.0C;

[0286] Charged from 10% SOC to 20% SOC at a constant current of 5.0C;

[0287] Charged from 20% SOC to 30% SOC at a constant current of 5.0C;

[0288] Charged from 30% SOC to 40% SOC at a constant current of 5.0C;

[0289] Charged from 40% SOC to 50% SOC at a constant current of 4.4C;

[0290] Charged from 50% SOC to 60% SOC at a constant current of 3.6C;

[0291] Charged from 60% SOC to 70% SOC at a constant current of 3.0C;

[0292] Charged from 70% SOC to 80% SOC at a constant current of 2.5C;

[0293] Charged from 80% SOC to 90% SOC at a constant current of 1.3C;

[0294] Charged from 90% SOC to 95% SOC at a constant current of 0.5C;

[0295] Charged from 95% SOC to 100% SOC at a constant current of 0.15C;

[0296] Then discharged from 100% SOC to 0% SOC at a constant current of 0.33C;

[0297] After 50 cycles according to the above charge and discharge strategy, the battery cell is charged to 100% SOC according to the corresponding charging strategy, and then the negative electrode sheet in the battery cell is disassembled, unfolded, and the lithium precipitation area is observed. The lithium precipitation area is the grayish white area on the negative electrode sheet, and the area of the lithium precipitation area is measured: when the area of the lithium precipitation area is less than 0.05% of the total area of the sheet, it is considered that there is no lithium precipitation; when the lithium precipitation area is greater than or equal to 0.05% of the total area of the sheet, it is considered that lithium precipitation occurs.

[0298] (4) Cycle performance test

[0299] Charge the battery monomer at 25°C to 3.65V at 1C, then constant voltage charge to 0.05C at 3.65V, next constant current discharge to 2.0V at 0.1C, record the discharge capacity D1 of the first cycle. According to the above steps, cycle 1000 times, record the discharge capacity Dn of the 1000th cycle. The cycle capacity retention rate of the battery after 1000 cycles = (Dn / D1)*100%.

[0300] (5) Safety performance test

[0301] Because of the negative and positive electrode tabs in the process of laser cutting tabs, each tab will have a left and right position deviation. When the negative and positive tab width is too large, the negative and positive tabs on the electrode assembly formed by the last winding will be too close, affecting the welding between the tabs and the adapter piece in the later stage. Therefore, there is a risk of tab delamination or tab lifting in the later cycle process.

[0302] Take 100 battery monomers, count the number of battery monomers that have tab delamination or tab lifting during or after the cycle process, and the tab delamination or tab lifting probability = (m / 100)*100%.

[0303] (6) Energy density test

[0304] Place the battery monomer at 25°C, charge at 0.33C constant current to 3.65V, then constant voltage charge to 0.05C, stand for 30min; discharge at 0.33C constant current to 2.0V, record the discharge capacity A0 at this time, unit: Ah; measure the length, width and height of the battery monomer using a caliper (generally calculate the size of the battery monomer shell, excluding the height of the electrode terminal, and excluding the insulating film outside the shell), calculate the volume V0 of the battery monomer, unit L; the battery monomer volume energy density VED = (A0 x discharge platform voltage) / V0, unit Wh / L.

[0305] Example 2-5

[0306] Prepare the battery monomer according to the same method as Example 1, except that when cutting the negative and positive electrode tabs, adjust the size w1 of the negative tab in the second direction and the size w3 of the positive tab in the second direction according to the following Table 1.

[0307] Comparative Example 1

[0308] The battery cell was prepared in the same manner as in Example 1, except that, when the negative electrode tab and the positive electrode tab were cut, the size w1 of the negative electrode tab in the second direction and the size w3 of the positive electrode tab in the second direction were adjusted according to the following Table 1 so that both w1 / w2 and w3 / w2 were 10%.

[0309] Comparative Example 2

[0310] The battery cell was prepared in the same manner as in Example 1, except that, when the negative electrode tab and the positive electrode tab were cut, the size w1 of the negative electrode tab in the second direction and the size w3 of the positive electrode tab in the second direction were adjusted according to the following Table 1 so that both w1 / w2 and w3 / w2 were 35%.

[0311] The battery cells prepared in Examples 2 to 5 and Comparative Examples 1 and 2 were tested for performance in the same manner as in Example 1. Table 1 below shows the relevant parameters of the electrode assemblies in Examples 1 to 5 and Comparative Examples 1 and 2, and Table 2 below shows the performance test results of the battery cells prepared in Examples 1 to 5 and Comparative Examples 1 and 2.

[0312] Table 1

[0313]

[0314] Table 2

[0315]

[0316] As can be seen from Table 1 and Table 2, by setting the ratio of the size w1, w3 of the negative electrode tab and the positive electrode tab in the second direction to the size w2 of the electrode assembly in the second direction to be within the range of 15%-30% in Examples 1-5, the internal resistance of the battery cell can be significantly reduced, the lithium precipitation can be improved, and thus the fast-charging performance and the cycle performance of the battery cell can be improved. In Comparative Example 1, since the ratio of the size w1, w3 of the negative electrode tab and the positive electrode tab in the second direction to the size w2 of the electrode assembly in the second direction is less than 15%, the size of the tab is too narrow to disperse the current well, and the electrode tab will precipitate lithium and have poor cycle performance. In Comparative Example 2, since the ratio of the size w1, w3 of the negative electrode tab and the positive electrode tab in the second direction to the size w2 of the electrode assembly in the second direction is greater than 30%, although it does not cause lithium precipitation, the positive electrode tab and the negative electrode tab are too wide, which makes the distance between the positive electrode tab and the negative electrode tab small, resulting in a greater probability of tab falling off and warping of the battery cell in the later stage.

[0317] Examples 6-8

[0318] The battery cell was prepared using the same method as in Example 1, except that when cutting the negative electrode sheet and the positive electrode sheet, the size L1 of the negative electrode film in the first direction and the size L2 of the positive electrode film in the first direction were adjusted according to Table 3 below.

[0319] Examples 9 and 10

[0320] Battery cells were prepared using the same method as in Example 1, except that the volume distribution particle size Dv50 and specific surface area of ​​the negative electrode active material graphite were adjusted according to Table 1 below.

[0321] Examples 11 and 12

[0322] Battery cells were prepared using the same method as in Example 1, except that the single-sided coating weight of the negative electrode film and the single-sided coating weight of the positive electrode film were adjusted according to Table 1 below.

[0323] Example 13

[0324] The battery cells were prepared using the same method as in Example 1, except that the cutting tool was changed when cutting the negative electrode sheets, so that after the cut negative electrode sheets were wound to form an electrode assembly, each layer of negative electrode sheets, except for the outermost negative electrode sheet, had one negative electrode tab. That is, except for the outermost ring, each ring of negative electrode sheets had two negative electrode tabs. The cutting tool was also changed when cutting the positive electrode sheets, so that after the cut positive electrode sheets were wound to form an electrode assembly, each layer of positive electrode sheets had one positive electrode tab. That is, each ring of positive electrode sheets had two positive electrode tabs.

[0325] The battery cells prepared in Examples 6 to 13 were subjected to performance tests using the same test methods as in Example 1. Tables 3 and 4 below show the relevant parameters of the electrode assemblies in Examples 6 to 13, and Table 5 below shows the performance test results of the battery cells prepared in Examples 6 to 13. For ease of comparison, the relevant parameters in Example 1 are also shown here.

[0326] Table 3

[0327]

[0328] Table 4

[0329]

[0330]

[0331] Table 5

[0332]

[0333] As can be seen from Tables 2-4, compared with Example 8, Examples 6 and 7 can significantly reduce the internal resistance of the battery monomer, improve the lithium precipitation condition, and thus improve the fast charging performance and cycle performance of the battery monomer by controlling the size L1 of the negative electrode film layer in the first direction to be less than 100 mm and the size L2 of the positive electrode film layer in the first direction to be less than 98 mm.

[0334] Examples 9 and 10 can reduce the internal resistance of the battery monomer, improve the lithium precipitation condition, and thus improve the fast charging performance of the battery monomer by controlling the volume distribution particle size Dv50 of the negative electrode active material graphite material to be 7 μm to 22 μm and controlling the specific surface area of the graphite material to be 0.8 m 2 / g to 2.5 m 2 / g.

[0335] Examples 11 and 12 can reduce the internal resistance of the battery monomer, improve the lithium precipitation condition, and thus improve the fast charging performance and cycle performance of the battery monomer by controlling the single-side coating weight of the negative electrode film layer and the positive electrode film layer to be within the above range.

[0336] Compared with Examples 1 to 12, Example 13 can further reduce the internal resistance of the battery monomer, improve the fast charging performance and cycle performance of the battery monomer by setting one negative electrode tab (i.e., two negative electrode tabs in one circle) for each layer of negative electrode tab in the electrode assembly except for the outermost circle, and setting one positive electrode tab (i.e., two positive electrode tabs in one circle) for each layer of positive electrode tab in the electrode assembly.

[0337] Examples 14 and 15

[0338] The battery monomer was prepared in the same manner as in Example 1, except that the mass ratio of the fluorine-containing sulfimide salt (LiFSi) and lithium hexafluorophosphate (LiPF6) in the electrolyte salt was adjusted according to the following Table 6.

[0339] Example 16

[0340] The battery monomer was prepared in the same manner as in Example 1, except that the electrolyte salt in the electrolyte was lithium bisfluorosulfimide, and the mass percentage of lithium bisfluorosulfimide in the electrolyte was adjusted according to the following Table 6.

[0341] Example 17

[0342] The battery monomer was prepared in the same manner as in Example 1, except that the electrolyte salt in the electrolyte was lithium hexafluorophosphate, and the mass percentage of lithium hexafluorophosphate in the electrolyte was adjusted according to the following Table 6.

[0343] Examples 18 and 19

[0344] The battery monomer was prepared in the same manner as in Example 1, except that the mass ratio of the carboxylic acid ester solvent and the carbonate solvent in the electrolyte was adjusted according to the following Table 6.

[0345] Examples 20-23

[0346] The battery cells were prepared according to the same method as Example 1, except that the types and mass proportions of the additives in the electrolyte were adjusted according to the following Table 6.

[0347] In Example 23, the additives included lithium difluoro(oxalato)borate, lithium tetrafluoroborate, a sulfur-containing additive, and vinylene carbonate, and the mass ratio of lithium difluoro(oxalato)borate, lithium tetrafluoroborate, vinylene carbonate, and the sulfur-containing additive was 1.5:2:4:1.

[0348] The battery cells prepared in Examples 14-23 were tested for performance according to the same test method as Example 1. Table 6 below shows the relevant parameters of the electrolyte in Examples 14-23, and Table 7 below shows the performance test results of the battery cells prepared in Examples 14-23. For ease of comparison, the relevant parameters in Example 1 are also shown here.

[0349] Table 6

[0350]

[0351] Table 7

[0352]

[0353]

[0354] As can be seen from Tables 6 and 7, in Examples 14-17, the electrolyte salt includes fluorine-containing sulfimide salt and / or lithium hexafluorophosphate, and the mass proportion of the electrolyte salt in the electrolyte is 10% to 20%, and when the electrolyte salt includes fluorine-containing sulfimide salt and lithium hexafluorophosphate, the mass ratio of the fluorine-containing sulfimide salt and lithium hexafluorophosphate is (1:4) to (4:1), which can significantly reduce the internal resistance of the battery cell, improve the lithium precipitation, and thus improve the fast-charging performance and cycle performance of the battery cell. Among them, compared with Example 1 and Example 14, the content of fluorine-containing sulfimide salt in Example 15 is higher, which will corrode the positive current collector aluminum foil, so the cycle performance of Example 15 is slightly worse than that of Example 1 and Example 14. Compared with Example 1 and Example 17, the content of the electrolyte salt in Example 16 is lower, so the DCR of the battery cell in Example 16 is slightly worse than that of Example 1 and Example 17.

[0355] In Examples 18 and 19, by controlling the solvent to include carboxylic acid ester solvent and carbonate solvent, and the mass ratio of the carboxylic acid ester solvent and the carbonate solvent is (1:6) to (1:1), the internal resistance of the battery cell can be significantly reduced, the lithium precipitation can be improved, and thus the fast-charging performance and cycle performance of the battery cell can be improved.

[0356] In embodiments 14 to 23, by controlling the additive to contain one or more of lithium difluoro(oxalato)borate, lithium tetrafluoroborate, a sulfur-containing additive, and vinylene carbonate, and by controlling the additive to be present in a mass percentage of 0.1% to 7% of the electrolyte, the internal resistance of the battery cell can be significantly reduced, the lithium precipitation can be improved, and thus the fast-charging performance and the cycle performance of the battery cell can be improved.

[0357] In addition, in embodiment 21, the additive is a sulfur-containing additive, and the amount of the additive is small. When tested by gas chromatography in reverse, the mass percentage of the sulfur-containing additive can be 0, i.e., the presence of the sulfur-containing additive in the electrolyte of the battery cell in embodiment 21 can not be detected.

[0358] Embodiment 22

[0359] The battery cell was prepared in the same manner as in embodiment 1, except that

[0360] The preparation process of the negative electrode tab was as follows:

[0361] The negative electrode conductive agent, super conductive carbon, and the negative electrode binder, styrene butadiene rubber SBR, were uniformly mixed in a mass ratio of 7:3 and dissolved in deionized water to form a negative electrode conductive slurry. The negative electrode conductive slurry was coated on the surface of a negative electrode current collector copper foil with a thickness of 4.5 μm, and after drying, a negative electrode conductive layer was formed, with a thickness of 0.5 μm. Then, the negative electrode slurry in embodiment 1 was coated on the surface of the negative electrode conductive layer and dried to form a negative electrode film layer. The negative electrode film layer was then subjected to processes such as rolling and cutting to form a negative electrode tab.

[0362] The preparation process of the positive electrode tab was as follows:

[0363] The positive electrode conductive agent, super conductive carbon, and the positive electrode binder, polyvinylidene fluoride, were uniformly mixed in a mass ratio of 7:3 and dissolved in N-methyl pyrrolidone to form a positive electrode conductive slurry. The positive electrode conductive slurry was coated on both sides of an aluminum foil with a thickness of 13 μm, and after drying, a positive electrode conductive layer was formed, with a thickness of 0.5 μm. Then, the positive electrode slurry in embodiment 1 was coated on the surface of the positive electrode conductive layer and dried to form a positive electrode film layer. The positive electrode film layer was then subjected to processes such as rolling and cutting to form a positive electrode tab.

[0364] Embodiment 23

[0365] The battery cell was prepared in the same manner as in embodiment 22, except that the coating process of the negative electrode conductive layer and the positive electrode conductive layer was adjusted so that the thickness of the formed negative electrode conductive layer and the positive electrode conductive layer was 5 μm.

[0366] The battery cells prepared in Examples 22 and 23 were tested for performance according to the same test method as in Example 1. Table 8 below shows the relevant parameters of the negative and positive conductive layers in Examples 22 and 23 and the performance test results of the battery cells prepared. For ease of comparison, the relevant parameters in Example 1 are also shown here.

[0367] Table 8

[0368]

[0369] As can be seen from Table 8, by providing the positive and negative conductive layers in the positive and negative electrode sheets and making the thickness of the positive and negative conductive layers in the range of 0.5-5 pm, the internal resistance of the battery cell can be further reduced, the lithium precipitation can be improved, and thus the fast-charging performance and cycle performance of the battery cell can be further improved.

[0370] Example 23

[0371] The battery cell was prepared according to the same method as in Example 1, except that:

[0372] 1) The positive active material was lithium iron phosphate doped with Al, V and Ti elements, wherein the content of Al was 410 ppm, the content of V was 1000 ppm, and the content of Ti was 400 ppm.

[0373] 2) Each positive electrode sheet after cutting included one positive electrode tab, and the width of the positive electrode tab (i.e. the dimension w3 of the positive electrode tab along the second direction) was 42 mm; each negative electrode sheet after cutting included one negative electrode tab, and the width of the negative electrode tab (i.e. the dimension w1 of the negative electrode tab along the second direction) was 42 mm; the dimension L1 of the negative film layer along the first direction was 94 mm; the dimension L2 of the positive film layer along the first direction was 89 mm;

[0374] The preparation process of the battery cell was carried out according to the following steps:

[0375] The above cut positive electrode sheet, separator and negative electrode sheet were stacked in order with the separator between the positive and negative electrode sheets to play a separating role, to obtain a core structure of a stacked structure, two core structures of the stacked structure were placed in mirror symmetry, the positive and negative electrode tabs were ultrasonically welded to the adapter piece and then folded and fixed with adhesive, then an insulating film was coated on the outside to form a double-wound core electrode assembly, next the double-wound core electrode assembly was placed in an outer shell, dried and then injected with electrolyte, and then subjected to vacuum packaging, standing, formation, shaping and other processes, to obtain a battery cell. The dimension w2 of the electrode assembly along the second direction was 200 mm, w1 / w2 was 21%, and w3 / w2 was 21%. The volume of the accommodation cavity was 1092 cm 3 , and the volume of the electrode assembly was 953 cm3 The volume ratio of the electrode assembly in the accommodation cavity is 87.3%.

[0376] Example 24

[0377] The battery cell was prepared in the same manner as in Example 23, except that,

[0378] The preparation process of the negative electrode tab was performed as follows:

[0379] The negative electrode conductive agent super conductive carbon and the negative electrode binder styrene butadiene rubber SBR were uniformly mixed in a mass ratio of 7:3 and dissolved in deionized water to form a negative electrode conductive slurry. The negative electrode conductive slurry was coated on the surface of the negative electrode current collector copper foil with a thickness of 4.5 μm, and after drying, a negative electrode conductive layer with a thickness of 3 μm was formed. Then the negative electrode slurry in Example 1 was coated on the surface of the negative electrode conductive layer and dried to form a negative electrode film layer; and then the negative electrode tab was formed through processes such as rolling, cutting, etc.

[0380] The preparation process of the positive electrode tab was performed as follows:

[0381] The negative electrode conductive agent super conductive carbon and the positive electrode binder polyvinylidene fluoride were uniformly mixed in a mass ratio of 7:3 and dissolved in N-methyl pyrrolidone to form a positive electrode conductive slurry. The positive electrode conductive slurry was coated on both sides of the aluminum foil with a thickness of 13 μm, and after drying, a positive electrode conductive layer with a thickness of 3 μm was formed. Then the positive electrode slurry in Example 1 was coated on the surface of the positive electrode conductive layer and dried to form a positive electrode film layer; and then the positive electrode tab was formed through processes such as rolling, cutting, etc.

[0382] Comparative Example 3

[0383] The battery cell was prepared in the same manner as in Example 23, except that, when cutting the negative electrode tab and the positive electrode tab, the size w1 of the negative electrode tab in the second direction and the size w3 of the positive electrode tab in the second direction were adjusted according to Table 9 below, so that w1 / w2 and w3 / w2 were both 12%.

[0384] Comparative Example 4

[0385] The battery cell was prepared in the same manner as in Example 23, except that, when cutting the negative electrode tab and the positive electrode tab, the size w1 of the negative electrode tab in the second direction and the size w3 of the positive electrode tab in the second direction were adjusted according to Table 9 below, so that w1 / w2 and w3 / w2 were both 36%.

[0386] The battery cells prepared in Example 23, 24 and Comparative Examples 3, 4 were subjected to performance tests according to the same test method as in Example 1. Table 9 below shows the relevant parameters of the electrode assemblies in Example 23, 24 and Comparative Examples 3, 4, and Table 10 below shows the performance test results of the battery cells prepared in Example 23, 24 and Comparative Examples 3, 4.

[0387] Table 9

[0388]

[0389] Table 10

[0390]

[0391] As can be seen from Table 9 and Table 10, by setting the ratio of the size w1, w3 of the negative and positive tabs in the second direction to the size w2 of the electrode assembly in the second direction within the above range in Example 23 and 24, the internal resistance of the battery cell can be significantly reduced, the lithium precipitation can be improved, and thus the fast-charging performance and the cycle performance of the battery cell can be improved. In Comparative Example 3, since the ratio of the size w1, w3 of the negative and positive tabs in the second direction to the size w2 of the electrode assembly in the second direction is less than 15%, the size of the tab is too narrow to disperse the current well, and the tab will precipitate lithium and have poor cycle performance. In Comparative Example 4, since the ratio of the size w1, w3 of the negative and positive tabs in the second direction to the size w2 of the electrode assembly in the second direction is greater than 30%, although it will not lead to lithium precipitation, since the positive and negative tabs are too wide, the distance between the positive and negative tabs is small, which leads to a greater probability of tab peeling and warping of the battery cell in the later stage.

[0392] In addition, by setting the positive and negative conductive layers in the positive and negative electrode tabs in Example 24, compared with Example 23, the internal resistance of the battery cell can be further reduced, and thus the fast-charging performance and the cycle performance of the battery cell can be further improved.

[0393] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A battery cell, characterized in that, The electrode assembly includes a negative electrode sheet; the negative electrode sheet includes a negative current collector and a negative electrode film layer, the negative current collector includes a negative current collection portion and a negative electrode tab extending out of the negative current collection portion in a first direction; the negative electrode film layer is located on at least one side of the negative current collection portion; The dimension w1 of the negative electrode tab in the second direction and the dimension w2 of the electrode assembly in the second direction satisfy: 15% ≤ w1 / w2 ≤ 30%; The first direction is the width direction of the negative electrode sheet, and the second direction is the length direction of the negative electrode sheet.

2. The battery cell according to claim 1, characterized in that, The dimension w1 of the negative electrode tab in the second direction and the dimension w2 of the electrode assembly in the second direction satisfy: 17% ≤ w1 / w2 ≤ 28%.

3. The battery cell according to claim 1 or 2, characterized in that, The negative electrode tab has a dimension w1 of 30 mm to 60 mm in the second direction.

4. The battery cell according to any one of claims 1 to 3, characterized in that, The negative electrode tab has a dimension w1 of 35 mm to 55 mm in the second direction.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The dimension L1 of the negative electrode film layer along the first direction is less than or equal to 100 mm.

6. The battery cell according to any one of claims 1 to 5, characterized in that, The negative electrode film layer has a dimension of 70 mm to 100 mm in the first direction.

7. The battery cell according to any one of claims 1 to 6, characterized in that, The electrode assembly includes a stacked structure and / or a wound structure.

8. The battery cell according to any one of claims 1 to 7, characterized in that, The electrode assembly includes a wound structure, and in the electrode assembly of the wound structure, except for the outermost negative electrode sheet, each layer of the negative electrode sheet includes a negative electrode tab extending along the first direction.

9. The battery cell according to any one of claims 1 to 8, characterized in that, In the fully discharged state, the thickness of the negative electrode film layer on one side is less than or equal to 80 μm.

10. The battery cell according to any one of claims 1 to 9, characterized in that, In the fully discharged state, the thickness of the negative electrode film on one side is 47 μm to 75 μm.

11. The battery cell according to any one of claims 1 to 10, characterized in that, The single-sided coating weight of the negative electrode film is 100 mg / 1540.25 mm. 2 Up to 160mg / 1540.25mm 2 .

12. The battery cell according to any one of claims 1 to 11, characterized in that, The compaction density of the negative electrode sheet is 1.3 g / cm³. 3 Up to 1.75 g / cm 3 .

13. The battery cell according to any one of claims 1 to 12, characterized in that, The negative electrode film layer includes a negative electrode active material, which includes graphite material, and the volume distribution particle size Dv50 of the graphite material is 7 μm to 22 μm.

14. The battery cell according to any one of claims 1 to 13, characterized in that, The specific surface area of ​​the graphite material is 0.8 cm². 2 / g to 2.5cm 2 / g.

15. The battery cell according to any one of claims 1 to 14, characterized in that, The OI value of the negative electrode is 8-14; wherein, the OI value of the negative electrode is the ratio of the diffraction peak area corresponding to the (003) crystal plane and the (110) crystal plane of the negative electrode active material in the XRD diffraction spectrum of the negative electrode.

16. The battery cell according to any one of claims 1 to 15, characterized in that, The porosity of the negative electrode sheet is 23%-36%.

17. The battery cell according to any one of claims 1 to 16, characterized in that, The electrode assembly further includes a positive electrode sheet, which includes a positive current collector and a positive electrode film layer. The positive current collector includes a positive current collection portion and a positive electrode tab extending out of the positive current collection portion along the first direction. The positive electrode film layer is located on at least one side of the positive current collection portion. The dimension w3 of the positive electrode tab in the second direction and the dimension w2 of the electrode assembly in the second direction satisfy: 15% ≤ w3 / w2 ≤ 30%.

18. The battery cell according to claim 17, characterized in that, The dimension w3 of the positive electrode tab in the second direction and the dimension w2 of the electrode assembly in the second direction satisfy: 17% ≤ w3 / w2 ≤ 28%.

19. The battery cell according to claim 17 or 18, characterized in that, The positive electrode tab has a dimension w3 of 30 mm to 60 mm in the second direction.

20. The battery cell according to any one of claims 17 to 19, characterized in that, The electrode assembly includes a wound electrode assembly, wherein each layer of the positive electrode sheet includes a positive electrode tab extending along the first direction.

21. The battery cell according to any one of claims 17 to 20, characterized in that, The dimension L2 of the positive electrode film layer in the first direction is less than or equal to 98 mm.

22. The battery cell according to any one of claims 17 to 21, characterized in that, The thickness of the positive electrode film on one side is 58 μm to 93 μm.

23. The battery cell according to any one of claims 17 to 22, characterized in that, The single-sided coating weight of the positive electrode film is 220 mg / 1540.25 mm. 2 Up to 350mg / 1540.25mm 2 .

24. The battery cell according to any one of claims 17 to 23, characterized in that, The compaction density of the positive electrode sheet is 2.4 g / cm³. 3 Up to 2.75 g / cm 3 .

25. The battery cell according to any one of claims 17 to 24, characterized in that, The positive electrode film layer includes a positive electrode active material, which includes a lithium phosphate with an olivine structure.

26. The battery cell according to claim 25, characterized in that, The positive electrode active material includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium nickel phosphate, lithium cobalt phosphate, and modified forms of any of the aforementioned substances.

27. The battery cell according to claim 25 or 26, characterized in that, The positive electrode active material includes modifying elements, which include one or more of Al, V, Ti, Zr, Hf, Ge, and Sn.

28. The battery cell according to claim 27, characterized in that, The modifying elements include Al, V, and Ti.

29. The battery cell according to claim 27 or 28, characterized in that, The modified element has a mass ratio of 100ppm-5000ppm in the positive electrode active material.

30. The battery cell according to any one of claims 17 to 29, characterized in that, The negative electrode further includes a negative conductive layer, which is located between the negative current collector and the negative electrode film; and / or, the positive electrode further includes a positive conductive layer, which is located between the positive current collector and the positive electrode film.

31. The battery cell according to claim 30, characterized in that, The thickness of the negative electrode conductive layer is 0.1 μm-5 μm; and / or, the thickness of the positive electrode conductive layer is 0.1 μm-5 μm.

32. The battery cell according to any one of claims 1 to 31, characterized in that, It also includes an electrolyte, which comprises a lithium-containing electrolyte salt; The lithium-containing electrolyte salt includes one or more of fluorosulfonyl imide salts and lithium hexafluorophosphate.

33. The battery cell according to claim 32, characterized in that, Based on the total mass of the electrolyte, the lithium-containing electrolyte salt accounts for 10% to 20% of the total mass.

34. The battery cell according to claim 32 or 33, characterized in that, The lithium-containing electrolyte salt comprises a fluorosulfonyl imide salt and lithium hexafluorophosphate; based on the total mass of the lithium-containing electrolyte salt, the mass ratio of the fluorosulfonyl imide salt to the lithium hexafluorophosphate is (1:4) to (4:1).

35. The battery cell according to any one of claims 32 to 34, characterized in that, The electrolyte includes a solvent, which includes carboxylic acid ester solvents and / or carbonate solvents.

36. The battery cell according to claim 35, characterized in that, Based on the total mass of the electrolyte, the solvent accounts for 73% to 89.95% of the total mass.

37. The battery cell according to claim 35 or 36, characterized in that, The lithium-containing electrolyte salt includes carboxylic acid ester solvents and carbonate solvents; based on the total mass of the solvents, the mass ratio of the carboxylic acid ester solvents to the carbonate solvents is (1:6) to (1:1).

38. The battery cell according to any one of claims 32 to 37, characterized in that, The electrolyte includes additives, which include one or more of lithium salt additives, carbonate additives, and sulfur-containing additives.

39. The battery cell according to claim 38, characterized in that, The additive accounts for 0.1% to 7% of the total mass of the electrolyte.

40. The battery cell according to claim 38 or 39, characterized in that, The additives include lithium salt additives; based on the total mass of the electrolyte, the mass percentage of the lithium salt additives is 0.1% to 3%.

41. The battery cell according to any one of claims 38 to 40, characterized in that, The lithium salt additives include one or more of lithium difluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, and lithium dioxalate borate.

42. The battery cell according to any one of claims 38 to 41, characterized in that, The lithium salt additives include lithium difluorooxalate borate; Based on the total mass of the electrolyte, the lithium difluorooxalate borate accounts for 0.1%-1.5% of the total mass.

43. The battery cell according to any one of claims 32 to 42, characterized in that, The conductivity of the electrolyte is 10 mS / cm to 20 mS / cm.

44. The battery cell according to any one of claims 1 to 43, characterized in that, The electrode assembly further includes an isolation membrane, which includes a base film and a coating disposed on at least one side of the base film; the coating includes a ceramic coating and an aqueous adhesive layer, wherein the ceramic coating is disposed between the base film and the aqueous adhesive layer.

45. The battery cell according to claim 44, characterized in that, The ceramic coating comprises a ceramic material, which includes one or more of the following: alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

46. ​​The battery cell according to claim 44 or 45, characterized in that, The water-based adhesive layer includes an adhesive material, which includes one or more of polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer.

47. The battery cell according to any one of claims 44 to 46, characterized in that, The thickness of the base film is 5 μm to 10 μm; and / or, the thickness of the coating on one side is 0.5 μm to 3 μm.

48. The battery cell according to any one of claims 44 to 47, characterized in that, The porosity of the isolation membrane is 20% to 60%.

49. The battery cell according to any one of claims 1 to 48, characterized in that, The battery cell includes a housing and a cover assembly, the cover assembly being disposed at at least one end of the housing, the housing and the cover assembly defining a receiving cavity, the electrode assembly being disposed within the receiving cavity, and the housing wall thickness of the battery cell having a large surface area of ​​0.4 mm to 0.65 mm.

50. The battery cell according to claim 49, characterized in that, The cover plate assembly includes a cover plate, a first electrode terminal, and a second electrode terminal, wherein the polarities of the first electrode terminal and the second electrode terminal are opposite; the minimum cross-sectional area S of the first electrode terminal and / or the second electrode terminal satisfies: 600 mm². 2 ≤S≤1100mm 2 .

51. The battery cell according to claim 49 or 50, characterized in that, The electrode assembly occupies 75%-90% of the volume within the receiving cavity.

52. The battery cell according to any one of claims 49 to 51, characterized in that, The electrode assembly occupies 80%-88% of the volume within the receiving cavity.

53. A battery device, characterized in that, Includes the battery cell according to any one of claims 1 to 52.

54. An electrical appliance, characterized in that, Includes the battery device as described in claim 53.

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